I dumped the database of the bug-tracking and code review systems we used, and analyzed those, by developer, matching them up to the same kind of deep analysis of subversion commits i used to look at coding productivity. This was a 5 year project with something like 60 devs. So yeah, I can know that.

BTW, if you think I can know that, you also seem to think that it's ok to say someone is 10X better than someone else at something that can't be measured.