Horse Names with Numbers?

I hope this isn't too stupid of a question, but after spending all week watching show jumping at The Royal, I've noticed a handful of international riders use horses with numbers in their name. For example some of the names were:

Larry 0146
Tosca 290
Nemo 119

What do those numbers mean? I bounced this question off a few other riders and they had no idea... just that it meant something, obviously. =)

The numbers and their significance depend on the breed of the animal and its registry.

Dutch Friesian stallions are all numbered, because that indicates they're approved breeding animals for the Dutch registry.

I believe the Hanoverian and similar registries do something along the same lines. Were these horses all stallions?