Attribution Window Mismatch
Google Ads, Meta, and TikTok each apply different default attribution windows. A user who interacts with your Google search ad, your Meta retargeting campaign, and your YouTube awareness ad before converting will appear in the attributed conversion counts of all three. Your MTA tool will apply a different model on top — linear, time-decay, or data-driven — producing a fourth attribution. The structural over-count in a five-channel US paid media stack can routinely exceed 200% of actual conversion volume before any configuration error is introduced.