May be lost or have been lost? Have there been attempts to 'find' them in e.g. server backups or consulting Simple Machines? It looks like there is quite a few that are not accessible anymore, new forum software or not, but perhaps your fatalism is premature?
Not quite fatalism on my part, reality.
Software is corrupt, images inaccessible so recovery is a challenge the powers that be don't want to peruse or can't. Hence the new software decision.
I, personally have looked and tried, but it is beyond my access to salvage the things you are requesting.
It is unfortunate, but there we are.