I'll keep the last branchpoint of each branch for the initial import
Won't work either... Sometimes we reuses merge labels in non-obvious ways. top-200501-merge and top-200502-merge both exist, the two were used for, say, treeprofiling, and then a random other (important) branch uses the first for its merge.
Also, even if you could track those down (you can't), it still would obliterate merge auditing, which is a very useful feature to find how exactly how someone screwed up a past merge.
I don't see the advantage of wiping those labels yet.
If you left all labels mentioned in any log entry, that would almost solve most instances that I know about, but, sometimes people misspell the tags in obvious ways in the log messages.
