Yes, if that is considered canon, Buffy is Giles' first Slayer. His first reaction is "What kind of name is Buffy?!" I love that comic! 🙂After reading "The Origin" comic series, yes, Buffy is Giles' first Slayer
I dont think the tv series is meant to be a continuation of the movie, she was 18 in the movie and 16 in season 1.
Whedon stated: "The origin comic, though I have issues with it, CAN pretty much be accepted as canonical. They did a cool job of combining the movie script (the SCRIPT) with the series, that was nice, and using the series Merrick and not a certain OTHER thespian [referring to Donald Sutherland] who shall remain hated." [1]