BASE_VER is bumped in SVN immediately after the release has been made, so the svn branch probably does say 4.9.1.
This should really be called 4.9.1-pre+svn211054.
Yes, I plainly agree. We use the BASE_VERSION number for reference, but it's indeed confusing, I like the 4.9.1-pre+svn211054 format.
Thanks Yvan