you have found help , welcome to the community-forum.
There are two different JBoss distributions
1) the community with releases like 4.2.1, 4.2.2, 4.2.3 and so on for different releases.
This version is open source without any professional support, you might get help here or not.
New and experimental features might raise here earlier.
2) The EAP (Enterprise Application Platform) version will count 4.2.0, 4.3.0 with a CP number (Cumulative Patch)
This version is only available if you have a support contract with RedHat (or as evaluation version).
The version have a more stable release and test cycle, you get updates for previous versions and, in case of bugs, a special patch for your version in production.
Because of this a 4.2.0.GA_CP0x might be newer as the 4.2.3(community).
I hope this will make it clear for you.