This web page says: “Service Release 6a.”
If you wonder if you have got “Service Release 6a”, compare your update date with date posted here: Bongo 2.0 Development [McNeel Wiki]
Your update date is displayed when you type BongoAbout.
By the the way, I wonder who needs “Service Release 6a.” Isn’t date good enough?
In the download is called 6a because we made some improvements to the CheckforUpdates -system, that’s the only difference from the original SR6 insaller.