As already reported at the announcement the new version is not called Acrobat XII but Acrobat DC. DC does not stand for the version number (roman DC equals 600) but means Document Cloud and is part of the product name.
The official version appelation is 2015 Release. In the PDF files created with this version, only 15.x.xxxxx is mentioned:
Adobe is changing to the year for the version number like in Creative Cloud. Already there has been a lot of confusion e.g. when in 2/2015 the InDesign update 2014.2 was released.
Acrobat XII (12), XIII (13) und XIV (14) will never exist. Perhaps Adobe tries to break the ban that in the past (at least since Acrobat 6) every even version number did a new user interface not bring much benefits. 😉