For Growth's account creation form v1 experiment (the one that's possible now thanks to T421972) to be analyzed properly in GrowthBook, I'll need to do the switch experiment assignments to use exposure events (T421740). However, while Growth's experiment logs exposure, the logged in/out retention rate AA instrumentation doesn't. Hence https://gerrit.wikimedia.org/r/c/mediawiki/extensions/WikimediaEvents/+/1269590 (T422823)

Solution: Temporarily modify the query which populates experiment_assignment_v1 to use experiment_exposure events in general and use page-visited events for experiments which start with "logged-out-retention" – a kind of backwards compatibility.

This solution:

• Does not require backporting code
• Does not require delaying Growth's experiment
• Is easily reversible after the aforementioned patch is deployed