Were you able to verify that the slides were manufactured here?
Looks to me like the USA Glocks have a "Georgia" stamp where the Glock stamp is on an Austria gun (left and just below the extractor). Four letters in the SR#, the Georgia stamp (state outline with a P in it), and USA on the slide by the model means made here. Now, if they put those marks on a slide made in Austria for a USA made frame is another matter.