Board Thread:Technical Updates/@comment-126761-20180124213059/@comment-5288784-20180207212822

Abeserra wrote: I believe that Wikia has a central database for all users. […]

This explains why you don't have to register to every wiki you want to edit, but you use an only one wikia user for all the wikis. Perhaps they do store some info on the users centrally, but I doubt it includes all the local rights you have on every wiki.