Sadly, the one thrift store we had that had pre-recorded tapes shut down a few years ago, and the local thrift store only carries commercial tapes (the usual suspects like Jerry Maguire, Men in Black, 90s Disney clamshells, etc). As for my experience:
A tape covered with pictures of the rock band Poison. Thought it would have contained vintage music videos and mtv footage, but it was just the 1997 Shining miniseries, with only 3 music videos and one mtv ad break at the very end (but at least they were from 1991).
A tape that said "Anime" and had Fatal Fury, Urusei Yatsura, and Gall Force: Eternal Story listed on it, but the first half of the tape was just Kim Possible: So the Drama (with commercials, they looked to be adverstising Phineas and Ferb as a new show, so it must be from the late 2000s), some episodes of My Gym Partner's a Monkey, and the last hour of Gall Force (taped off sci-fi, but sadly, no commercials).
A tape that claimed to have wrestling footage from 1997. The first 2 hours were taped over with NBA highlights (not even a full game), but the rest was intact, including 2 Pay Per Views. However, to fit all the content onto one tape, the ring entrances and interviews were snipped out by the person recording, as well as, sadly, all the commercials.
Another thing to try, though it wont be as interesting, is unlabeled audio tapes.
