---
title: "When 13F Reported Value Lies: The BRK/A and 5 Other Traps"
type: learn
slug: 13f-reported-value-traps-brk-a-options-market-maker-aum-mismatch
canonical_url: https://13finsight.com/learn/13f-reported-value-traps-brk-a-options-market-maker-aum-mismatch
published_at: 2026-05-11T12:47:09.289Z
updated_at: 2026-05-11T12:47:12.486Z
author: Sarah Mitchell
author_title: Education Editor
author_url: https://13finsight.com/authors/sarah-mitchell
word_count: 1361
locale: en
source: 13F Insight
---

# When 13F Reported Value Lies: The BRK/A and 5 Other Traps

> 13F filings report dollar value across millions of institutional positions, but the headline number can wildly mismatch economic ownership. Six common traps — Berkshire Class A's per-share price distortion, options notional reporting, market-maker inventory, and others — that every reader should learn to spot before drawing portfolio inferences.

A 13F filing's headline number — total reported value — looks like a straightforward dollar measurement of what an institutional filer owns. Most of the time it is. But a non-trivial percentage of 13F filings have at least one structural distortion baked into the dollar figure that turns the simple read into a misleading one. This guide walks through six traps we've seen in our own data this quarter, with examples drawn from the recent research articles on our platform.Reading 13F data well means catching these before they shape an investment thesis.Trap 1: The BRK/A Per-Share Price DistortionBerkshire Hathaway Class A shares trade for roughly $725,000 per share. A 13F filer holding even a single Class A share will report ~$725k of dollar exposure on that one line. A filer holding 365 Class A shares reports $264.6B — which can dominate a filing for a manager whose actual US equity book is $36B of operating positions plus a strategic small block of Berkshire.We saw exactly this in Mirae Asset Global Investments' 2026Q1 13F: total reported value jumped to $299.33B from $36.04B in 2025Q4, driven entirely by a 365,000-share Berkshire Class A line at $264.6B (88.76% of the book). The actual portfolio decisions Mirae made between quarters didn't change materially. The reported value did.The fix: When you see a top-weight position in BRK/A at an absurd dollar value with high portfolio percent (>50%), compute the implied share count. If it's a small block of Berkshire Class A held alongside an otherwise diversified book, anchor your analysis on the rest of the holdings, not on the dollar headline. The same applies to NVR (NV Homes Class A, ~$10,000/share), AZO (AutoZone, ~$3,000/share), and other ultra-high-priced names — but BRK/A is by far the most common source of this trap.Trap 2: Options Notional Reporting (Market Makers)Market makers like Citadel Securities, Susquehanna International Group, Jane Street, and Optiver report option positions at notional exposure, not economic AUM. A market maker holding $9B of NVDA call options as a hedge for short volatility positions will surface in our holdings table as a $9B 'NVDA position' — but they are not making a directional bet on Nvidia. They are running an options book.The platform's filer classification system tags these entities as market_maker and excludes them from smart-money signal surfaces. But the raw 13F reported value still includes them. Article authors who write 'Susquehanna's $9B NVDA position is the largest bullish bet in the table' have made a category error. Susquehanna is not bullish on NVDA; Susquehanna is hedged.The fix: Always check the filer's classification before treating top-line dollar weight as conviction. We covered this directly in our recent AMD Q1 earnings holder-base read — Jane Street and Susquehanna combined held $18B of AMD, but the structural meaning of that position is materially different from an equivalent stake at an active asset manager.Trap 3: Index-Fund Mandates Mistaken for ConvictionThe three largest 13F filers — BlackRock, Vanguard, and State Street — together account for roughly 30%+ of disclosed institutional ownership in US large-cap equities. They are passive index funds; their position sizes are determined by S&P 500 weights, not by views on individual stocks. When a retail-investing piece reads 'BlackRock is the largest holder of XYZ stock,' the structural meaning is 'XYZ is in the S&P 500 and BlackRock runs iShares Core S&P 500 ETF.'The platform flags these filers with passive_index classification: BlackRock Fund Advisors, Vanguard, State Street SSGA, Geode Capital Management, Northern Trust, and Schwab Investment Management. Active conviction signals live further down the table at active asset managers — Fidelity, Capital Research, Wellington, Norges Bank — whose position sizes reflect actual investment decisions.The fix: Strip out the passive overlay before computing 'institutional conviction.' Our recent NVDA holder-base read showed that ~$1.2T of NVDA's top-20 dollar weight is passive mandate money — meaningful for the index but uncorrelated with conviction in the May 20 earnings print.Trap 4: Custodial Holdings (Bank Trusts)Large bank trust departments — State Street Bank custody, BNY Mellon custody, Northern Trust custody — file 13Fs reporting client assets held in custody, not the bank's own position. A bank custody arm with $50B of disclosed Apple holdings is holding that AAPL on behalf of clients (pension funds, family offices, registered investment advisors) who individually file or are exempt from 13F.The platform classifies these entities as custodian. They appear in our holdings tables for transparency, but they should not be read as institutional conviction.The fix: Bank-name filer entries in a holdings table that include 'Trust', 'Custody', 'Wealth Management' in the name are usually custodial — verify the classification before drawing inference. Active asset management entities at the same parent bank file separately and are the conviction read.Trap 5: Dual-Class Share Structures and Form 4 'Sold Everything' MisreadingsThis trap is more common on the insider-data side than the 13F side, but it's worth surfacing because the analytical error mode is similar. When an insider's Form 4 Table I shows sharesOwnedAfter: 0 on a sale of Class A common stock, the natural reading is 'sold all shares.' That reading is wrong any time the insider holds Class B (super-voting), preferred, or trust-structured positions, all of which surface in Form 4 Table II rather than Table I.The Mark Zuckerberg / Meta case is the canonical example: he can sell all his Class A and report 'shares owned after: 0' while still controlling roughly 50% of voting power via Class B. The platform flags these cases with a MULTI-CLASS marker on the pre-publish checks — but raw Form 4 readers still trip on it.The fix: Before asserting an insider 'exited' a position, verify Form 4 Table II and the company's most recent proxy statement for dual-class holdings.Trap 6: Quasi-Passive Filers (Quant Index, Smart Beta)Dimensional Fund Advisors, Research Affiliates, and other quasi-passive filers run rules-based or factor-tilted strategies. Their position sizes are determined by mechanical factor exposures (value, momentum, low-vol), not by individual stock conviction. The platform tags them as quasi_passive.A quasi-passive position move from quarter to quarter usually reflects factor rebalancing, not a thesis change. Article authors who write 'DFA increased its AAPL position by 12% — signaling a quality-tilt rotation' should verify whether the change is consistent with the factor rules underlying that DFA product, not the analyst's preferred narrative.The fix: Quasi-passive filer moves should be cross-checked against the factor strategy disclosed in the fund family's prospectus. If a position change is mechanically explained by the strategy's rules, it's not active conviction.The Universal PatternEvery one of these six traps shares a structural property: the reported dollar value answers a different question than the analytical reader assumes. The dollar value tells you what was disclosed under SEC reporting rules. It does not tell you what the filer believes about the stock, what economic exposure the filer holds, or how the position will respond to future events.The reliable analytical anchors are:Filer classification (active vs. passive vs. market_maker vs. custodian vs. quasi_passive)Position concentration relative to benchmark weightsQuarter-over-quarter changes net of mark-to-marketCross-references to 13D/G filings (which carry binding intent declarations)Form 4 transaction codes (S vs. P vs. M vs. F vs. A vs. G)The headline 13F dollar number alone, without these anchors, is a half-told story. The smart-money signal feed applies the filer-classification framework upstream so that the surfaces — Smart Alerts, Whale Score, Combined Holdings — only show positions whose dollar weight is informative. The research hub applies the same framework to individual filer write-ups.FAQDoes this mean BlackRock and Vanguard 13Fs are useless?No — they're useful for measuring float ownership concentration, for understanding index inclusion effects, and for tracking the passive flow trends that move whole sectors. They're just not useful for inferring conviction on individual names.How do you distinguish a market-maker hedge position from a directional active book?Filer classification (we tag market_maker explicitly), business model (regulated broker-dealer vs. registered investment advisor), and option concentration in the 13F itself. A filer reporting >40% of disclosed value in single-name options is almost certainly hedging, not direction-betting.Why do you still show passive filers in holdings tables?Transparency. Some readers want to see the full ownership picture including the passive overlay. The filter is applied at the analytical-signal layer (Smart Alerts, Whale Score), not at the data-display layer.

## FAQ

### Why does a 13F's reported dollar value sometimes mislead?

13F reported value answers a different question than 'what does this filer believe about the stock.' Six common distortions — Berkshire Class A's per-share price, market-maker option notional, index-fund passive mandates, bank custody holdings, dual-class share structures, and quasi-passive factor strategies — can make the headline number mismatch economic conviction.

### What is the BRK/A 13F reporting trap?

Berkshire Hathaway Class A shares trade for ~$725,000 each. A 13F filer holding a small block of Class A — say 365 shares — reports $264.6B of exposure on that one line, which can dominate the filing's total. Mirae Asset's 2026Q1 filing showed exactly this: a $264.6B Berkshire line at 88.76% of an otherwise $36B portfolio.

### How do you identify a market-maker 13F filing?

13F Insight tags filers explicitly with classifications including 'market_maker' (Susquehanna, Jane Street, Citadel Securities, Optiver, CTC, Wolverine, PEAK6). Structural giveaways: regulated broker-dealer license, high option concentration in the filing, and reported value that scales with market-wide options volume rather than fund AUM.

### Why does our platform exclude passive funds from 'smart money' surfaces?

Passive index funds (BlackRock, Vanguard, State Street, Geode, Northern Trust, Schwab IM) hold positions because of index mandates, not active conviction. Their position size reflects S&P 500 weighting, not analyst views. The EXCLUDED_FILER_TYPES_FOR_SMART_MONEY filter is applied at the analytical layer.

### How do dual-class share structures cause Form 4 misreadings?

When a Form 4 Table I shows 'sharesOwnedAfter: 0' on a Class A sale, the natural reading is 'sold everything.' That reading is wrong if the insider holds Class B (super-voting), preferred, or trust-structured positions — which surface in Table II rather than Table I. Always cross-check the proxy statement before asserting an exit.

### What are quasi-passive filers and how should I read their position moves?

Quasi-passive filers like Dimensional Fund Advisors and Research Affiliates run rules-based factor strategies (value, momentum, low-vol). Position size changes typically reflect factor rebalancing rather than active conviction. Verify quarter-over-quarter moves against the strategy's published rules before reading them as a thesis change.

---

Source: 13F Insight — https://13finsight.com/learn/13f-reported-value-traps-brk-a-options-market-maker-aum-mismatch
Author: Sarah Mitchell — https://13finsight.com/authors/sarah-mitchell
Last updated: 2026-05-11T12:47:12.486Z