
I think Reino has answered your initial question. Great link to the WaA codes as well!!
The three letter code is a separate thing to the WaA mark, I wasnt aware that a list existed for the WaA inspectors mark, but you can see from the list that Reino posted that the inspectors were not tied to just one factory, so for identification of the factory the three letter code is better.
I hope this all helps
regards Kev