All Pro Tools 7.x and higher sessions have a +12 dB fader gain level. However, when saving a Pro Tools 7.x or higher session to a lower version of Pro Tools that supports +6 dB and +12 dB fader gain, the new session can be saved with either a +6 dB or a +12 dB maximum fader gain.
When saving a +12 dB session as a +6 dB session, Pro Tools alerts you that any automation settings over +6 dB will be lowered to +6 dB. See
Saving a Copy of a Session.
In Pro Tools 7.x or higher, when opening a session that was saved with a +6 dB maximum gain level, the session will update to a +12 dB range.