Back in 2002 I ordered a new G17 from a wholesaler. When it came in the serial number on the sticker on the carrying case, the barrel, the slide, and the manilla envelope with the fired case was FBZ004. The serial number on the frame was FBZ003.
Somebody at Glock switched uppers and lowers with FBZ003 and 004, which means the other one with swapped parts is out there somewhere.
How's that for consecutive numbers?
Martyj, you asked if it was hard to come by consecutive numbers. Naw, it was easy.