What, if anything, came of this discussion? Since Trakt adamantly refuses to support plays without a timestamp (requested in several places over the years, now canonically here), the best workaround we all had to track things from before we joined the site was to pick some past date.
This deduplication has wiped out all of the extra plays I added for shows or movies I watched repeatedly, for example reducing my play count of every pre-Discovery Star Trek series from 4-5+ to 2 or 3. I could go back and re-add things with the times incremented by 1 minute for each repetition, but I’d like to find out if there’s any forthcoming solution first.