Thanks for the reply Dan.
That wasn't quite what I was looking for. I'll demonstrate with the emoji numbers what I mean
2 3 4 5 6 7 8 9 10
2 3 4 5 6
7 8
9 10
Sometimes when there is an entry the 1 and 1a are on the inside, as in the 1st example. At other tracks they might appear similar to example 2.
What I am trying to find out is where can I find the information about how different tracks or racing juristictions decide on how the horse numbers are allocated to which stall.
Thanks.