Is it possible to find old posts/games
My finding are about five years it takes to lose critically dead games. It can take less time, but I've never seen it take more. It certainly may, but I also never reached nearly my GMing capacity, and also frequently repurpose boards rather than make new ones.
I'm a month late to the conversation, but my suggestion, from now on, is archive. Do so every time you kill a game, or need to prune a thread. You may think it unnecessary, and that's fine if you have no plan to reread the threads. Often times you'll be zealous when you kill or abandon a game, and regret your haste when RL circumstances improve, which is why every GM, myself included, terminates game; RL trouble. You will also be glad you did so frequently, if you suddenly have the WCS (worst case scenario); someone is in the hospital, missing, in prison, or died. During those times you want precursory measures, as that's no time to deal with RPoL, even though life (hopefully!) goes on and you eventually come back...only to find not a trace.
When you play, it's more difficult, but you can still archive the "hard" way if your GM follows the <1,000 post "rule" of a thread. I do this very often, and it's helped with a host of problems, from GMs deleting something and not remembering, or another player changing their tune on a vital topic and pretending like they were always so aligned.
Archiving is also a good test to see if you need something on a board you GM. If you can't be bothered to archive it, because it's too big, or there are too many threads, you probably can cut down on it, and jase and mods will appreciate it. If you don't use it, and have no need for it, it can probably be removed. I prefer to archive ANYTHING rather than just delete it. TBH though, I enjoy reading old threads though, even over a decade later. I have all but my first four game archived, and it's been great help for keeping a record of my own strengths and weaknesses.