Hello,
In fact it's the same process on every OP in-house caliber, the first notch serves to change the date (normaly) with hour-to-hour jump or ajusting time zone (like Patrick said) i.e. the first notch on the P9000 does it too.
There's a P2002 in the PAM 339, same caliber that PAM 268, PAM 233 etc..My guess is that Panerai did not remove (or forgot to remove) the first notch even the watch don't have the date fonction...
My 2 ct (and sorry for my bad english)