The entirety of the other forum is still available at the bottom of the forum index, just like the old phpBB archive was when we moved to IPB in 2006. Not to fear, absolutely nothing has been lost

. The old-school phpBB forums aren't currently accessible (that database is enormous and is going to take some serious brainstorming to keep available) but the IV you're used to is there in all its many-threaded glory ;-).
I cut this new forum down to the past two weeks+sticky posts because the sad truth of web forums is that, once the database gets so big, they're not maintainable. Searches take too long and too much CPU power, the RAM get tied up sorting through lots of irrelevant information, search indexes get unmanageably huge. Five years is a long time for a web forum when you're not constantly deleting old threads.
This time around, forums of little consequence
will be manually pruned. Seller forums, merch announcements, etc will only retain their posts for a month or two before inactive ones get deleted. Forums like the informatory will never be pruned, though.