I only know what I've read. That said, take a look at the FCC certification document for the ESP-12: https://fccid.net/number.php?fcc=2ADUIESP-12&id=253176
Notice that it is certified as a "single modular" device.
The FCC requires that single modular devices be totally self contained: http://www.lsr.com/white-papers/fcc-guidance-on-transmitter-... https://www.fcc.gov/oet/ea/presentations/files/oct09/Modular... [PDF]
The ESP-12 module does not have onboard voltage regulation. Thus, it is not totally self contained and its certification is meaningless.
Regardless of the above discussion, these modules do not have a marked FCC ID, so any certification they do or do not have is meaningless.
Like I said, I only know what I've read. I don't understand how they reached certification without onboard voltage regulation, but they did. I don't know if that means the certification will be voided, but I certainly wouldn't want to be selling a product using these modules right now.