The AS means that the DB 605A engine was "equipped" with the larger two-stage supercharger of the DB 603 one. Thanks to that The DB 605AS motor got about 880kW ( 1200 KM) at ceiling 8250 m. Also that was a much lighter device than the GM-1 system.
Correct. The G-10s were fitted with DB 605 D engines as standard.
A small batch of about 50 Erla built G-10s were fitted with the DB 605 ASM engine, presumably as a war time expedient, but were not officially designated /AS.
Identifying all these late war versions, many made up by upgrading older air frames is a bit of a minefield