When you try to add EAP 6.0.0 DR11 as a server in JBT it will display a warning:

This server type expects a version of 6. but the server directory is of version 7.1.0.CR1-redhat-1.

The same happens with DR12, but not DR8. I don't know where exactly JBT is looking for the version number within the AS directory (I was able to find 7.1.0.CR1-redhat-1 in many modules' config) but it seems the older DR releases probably showed version 6, but now they are derived from the JBoss AS version.