In this case I think you could use a .mailmap [1] in the repo to associate the old email addresses with current, verified addresses.
However, while this works for git (i.e., maps old address to new address in "git log" for example), GitHub does not seem to honor this file.
The other issue of course is that at this point in time, there would not be a .mailmap. Of course, github can then fall back to a .mailmap file in the latest commit of the main branch.