The linked article satisfies part of the question around why success conversions are still counted (90 Day Expiration)
I have a similar question, but unanswered is why Impressions are still being counted
The Activity in question was certainly set to Inactive and Archived, yet there is a small stream of impressions coming through daily. The volume (especially in the days immediately proceeding) is enough to make me ask
The linked A4T document says explicitly that Impressions should no longer be counted after the Activity is deactivated