Well they went off of the serial that I read to them. GFXXXUS....so now I'm more worried that I picked up a parts gun.
EDIT: just went to the following link
http://www.flarms.com/forums/showthread.php?113-Glock-Serial-Numbers and found out that it is in fact a Gen2 made in June of 89....this thing is almost as old as I am lol