(I found that out the hard way. When I had the old racing QH, I first called the Jockey Club - "That's not a Thoroughbred number," said they. Then I called the Standardbred association. Not a SB number either. Only THEN did I call AQHA . . . I mean, he was almost 17 hh and didn't have a big butt, the last thing on earth I was thinking was QH.)
Ah - good tip... I don't know how to interpret the numbers, but I know if you do know, you can tell their birth year from the number.