Volvos model years changed when they came back after the summer break, when the factory closed for maintainence.
PV544F August 1964 - August 1965 Chassis # 419300 - 436599 total 17300
PV544G August 1965 - October 1965 Chassis # 436600 - 440000 total 3401
Of the PV544G models only 19 had the G after the type number code i.e.11121G
All of the rest had F at the end, which means you'll need to confirm that it's a 1965 "G" by the chassis number.
I don't know which factories were making what in late '65 but I would hazard a guess that the PV factory quickly changed over to making the 144 which came out at about this time.