Undocumented deduplication

platform

Some ad platforms silently dedupe overlapping target geographies or audience segments across line items without disclosing the rule, causing reported vs. delivered reach to diverge in ways not explainable from inputs alone.

Detection

Delivered unique reach is materially lower than the sum of non-overlapping requested cells, with no documented overlap in the request.

Mitigation

Request a delivery-level (not planning-level) geography breakdown from the platform where available
Independently pre-dedupe overlapping targets before submission so platform behavior can't be blamed for the gap

Affected conversions

H3 → platform-native IDs approximate
Cell system → cell system approximate