I have heard that the offspring from a registered pony (reg. in what, I'm not sure) and a non-AMHR/AMHA mini can be registered into that pony registry. As long as one is registered (and DNAd I think(. Is that true?
I think what you are thinking of is the new National Show Pony Registry.....one parent must be either AMHR or ASPC registered and there is a DNA requirement I think for both parents of the foal to be registered......
Otherwise most of the pony registries are closed and there are quite a few breeds of ponies out there.
I understand it a bit different there must be one parent that is AMHR or ASPC reg the other parent can be any other breed. the resulting foal must measure in at 14.2 or under and the parent that is reg with AMHR or ASPC must be DNA'd as well as the foal but not the other parent of another breed