<b>Five alt-IDs, five different match rates</b>

<b>Five alt-IDs, five different match rates</b>

Watching: stacking multiple alternative IDs — UID2, ID5, RampID, a publisher first-party ID — doesn't stack match rates additively. Each bidder picks the one ID it trusts, so spreading signal across five graphs can lower the match rate any single buyer actually uses versus committing to one or two.

— More ID partners ≠ higher effective match
— Buyers consume one graph, not the union

Impact: check which alt-ID each top buyer actually bids on, then prune the dead-weight graphs. (sourced)