Andrew, it appears to me which the child board tip sounds like the most dependable option to maintain some kind of easily searchable variety of both resolves as well as unsolved queries.
Marking the subject line would still allow older, unsolved threads to fall away of view. I'm presuming which each user can move their particular threads from a deck to some other? Or perhaps, is this anything the mods/you would have to do?
Unfortunately, until someone has a fair number of posts they cannot modify their posts. It turned out to be a favorite tactic for spammers - create an innocent post, leave it for a while (even months) and then go back to edit it to add spam links. I was not able to find a function or mod for the forum that helped mitigate that.
Doing quite a bit of housekeeping to this part of the forum, moving solved threads to solved and unsolved ones to the unsolved archives, is on my list of things to do. Not going to happen until at least August based on my current duties, but I do try to work through ten or twenty now and then just to make some headway.