For BE you buy the number bib and when you go to the secretary they give you 2 paper printed numbers to slip inside your bib. These are also the perfect size to use for putting ice tight on your horse after you round.
Even local hunter trails round here are starting to use the BE style number bibs, the one i am thinking on caters for both but im sure that soon it will just be the BE ones. I got one cheap off ebay, i think its made by shires.