Distinguish three observations
The order book shows offered liquidity to the extent provided by the feed. The execution stream shows traded quantities. Delta classifies executions by aggressive side. A large resting limit can change or disappear before any trade occurs there.
An example without assuming a signal
A snapshot shows 200 contracts offered at one ask level. Later, 40 contracts trade there while the offered size changes. The first image proves neither that all 200 traded nor that a reversal will follow.
A review needs event sequence, data completeness and the observed price response. A concentration can motivate a review question; the subsequent direction must be documented independently.
Check entitlements and history
The ATAS connection does not replace exchange entitlements. Check the requested market, actual contract and available depth. Candle history is not complete historical level-2 data. Gaps should remain visible rather than being hidden by visually smooth data.