Hi Martin
Yep, probably in my haste to read the information, I did misunderstand what you were saying. My comprehension was possibly also "coloured" by the theory of the "letter" denoting a trade/region that I read somewhere.
I think that your idea makes a LOT more sense than the previous "theory" so a real, hearty "thanks" for a very readable, well-thought out piece.
If you really want to talk "unworkable" system
, I can talk about the system that was initially put in place for allocating WW1 service numbers to NZ servicemen. It did work, after a fashion, but only when they started from scratch and more or less gave up what was called the "bar" number. No this wasn't anything to do with the "wet canteen"
.....