What we found. An early look at a thin slice of the sample suggested one routing source (name withheld) delivered on its quotes less often at the $1M trade size than at $1k, pointing at a large-trade slippage problem. Instead of publishing, the claim was held until each measurement cell met a rating threshold: at least 30 realized samples spanning at least 7 days. With the full sample (916 rows over 9.6 days), the pattern reversed: the source realized 65.8% at $1k, 72.9% at $10k, 87.7% at $100k, and 90.7% at $1M. The $1M cohort was its best; retail-size quotes were the real weakness. That weakness held on every day of the sample rather than tracing to one bad run, no peer source shared it, and every miss was a real failure to deliver — not a benign routing artifact.
Why it matters. The thin-sample conclusion was not just imprecise — it pointed in the opposite direction of the truth, and it would have been published under the system's own name. Cohort comparisons on thin samples are the most dangerous class of data-product claim, because they are usually plausible, directional, and wrong.
Recommendation (adopted). Gate every published cohort comparison on the rating threshold, expose the threshold in the methodology, and treat "not yet rated" as a first-class published state rather than an excuse to ship the early number.