Are we looking at the same issue? https://jira.codehaus.org/browse/GEOT-4795
shows a comment in May 2014 (making 12-beta the first chance to try it out).
The versions for each jar we ship are included in the jar filename, or when using maven you can check what versions are being used by typing:
For online reference you can review the root "pom.xml" file which is what we use to configure which jars to use.
Hunting through this I can find:
This also serves an example of how you can control what version of a jar is used in your project.
Hope this helps for next time.