Around August 2015, the six alpha-numeric s Glock serial numbers ended with "ZZZ999".
I own a triple ZZZxxx G17 g4 grey frame, one of the last to get the shell casing. Anyway, Glock assigned the seven set (4-alphas and 3-numeric s) beginning with ""A"" to Glock USA.
Those serial numbers beginning with ""B"" are assigned to Austria. They are built concurrently. I do not know about South America or Dubai. Those maybe USA/Austrian imports for all I know.