HI Tberg: Can you read the numbers? Are they partial or full VINs? GM often stamped frames and other large parts with sequence numbers to make sure they came down the line in the correct order for assembly. Might be something like that if not a VIN.
I just went and checked the numbers
Drivers side trunk rail H 50 1
Pass. side trunk rail H 49 1
Drivers side front quarter A 12192 B
Pass side front quarter no numbers
All of these number dont jive with the VIN or the sequence number
if I had to guess that was a part # due to the sequential 49 & 50. they might also be what are called 'fiducial marks'? don't ask me I have no clue understanding what those are. however, if you go online to the GM Heritage site and download the Archive Vehicle Kit for your year/model, near the back you may find schematic drawings showing these marks and numbers.