For some reason I've yet to figure out, on both my test site and my main site, one of my authors had his post counts set to zero after I started adding Co-Authors profiles for other users... I hadn't even gotten to that account yet.
In the Posts listing, his name is still listed as the author, but in both the Users and Guest Authors listings (after I'd added him a few days later), it says he has zero posts.
Also, I need to change the ownership of a lot of articles, in order to assign them to a dummy user account so their guest author profiles will take over when I remove the real accounts those people don't need... but I can't seem to change the author of the posts anymore unless I individually edit each and every post. Author seems to have vanished as a editable option when in the Posts listings.
On a site with nearly 15k posts, that'd be a heinous process :)