Edit attribution for revisions converted from UseMod days or imported from another wiki are currently a little odd; the revision record stores an ID of 0 and the username directly.
We then can end up assigning those edits to whoever registers the account name locally... which usually is correct, but sometimes not. :)
It could be useful to be able to store some sort of source wiki identifier with that attribution, which might help with dealing with these cases; and might also be relevant for OpenID-type cross-wiki authentication situations.
On the other hand it might be really difficult to retrofit in. Needs some pondering...