We switched the bbs to vBulletin software 5 June 2005, hosted on a new account on a different server. We thought this would eliminate our need to purge the message base for the forseeable future. Our message base started over from scratch at that point because there was no way to carry over the messages from our previous board due to incompatibilities between the two systems.
But this server limited our database to only 100 mb, even though we had several gb of total disk space available. This necessitated continuing the pruning of forums just as we had to do with our former software and server, although we were able to maintain far more messages than on the previous system.
In addition there was a serious error that occurred in roughly August '05 in which all messages that were then in TUG Lounge were mysteriously wiped out. We still don't know how this happened.
We then acquired our own dedicated server hosted by Liquid Web, which we moved the bbs to on July 24, 2006. We were able to retain all existing messages through this move. We have a tremendous amount of disk space here, and we are still several years away from having to worry about running out of disk space. With the exception of some time dependent posts (like LMR offers), and some of the spam posts, nothing has been purged from the board since we went to the new server in late July '06.