My understanding of the error 12 issue is this:

Trying to log in to a different server than your home region.

Your account may be registered in NA, but you're trying to log in to Asia or EU server: error 12.

Is this a correct statement?

If so, it would explain why there are so many of these. Of course, the Asian servers are run by a different company (or two) than Blizzard.

The explanation:

Global play, as Blizz has already stated, will be available some time after 12:01 am PDT.