I have both of the sets of printed Studbooks originally put out by AMHA...the ones w/ the black covers and the ones with the tan covers(they messed up on the Black ones; left out the horses' colors, if I recall correctly(too lazy to go find them and check right now!)...so had to have them re-printed, and provide the 'corrected' version to all who had purchased the 'original' flawed set!! They are soft-cover, large and unwieldy, but a wealth of information!
Unfortunately(IMO, at least!),in the AMHA Studbook, the organization is alphabetical, by name, instead of numerically, by registration number(as with AQHA, where it is easy to find out that the King Ranch's stallion "Wimpy" was P-1, the first AQHA (Permanent, hence the "P")registration number issued, in honor of being named Grand Champion Stallion at the Ft. Worth Stock Show(I am relying on memory, so I *think* this is the case!)in @ 1940. The alphabetical listing makes it virtually impossible to determine what horse had the registration number "ONE" by looking through the printed AMHA Studbooks! Not sure if it could be found in the online form, as I no longer breed and don't pay for access to that...and I don't know the format of the AMHR Studbook, so can't speak to that.
Over time, there were other viable registries begun for miniature horses; one notably was the International Miniature Horse Registry(IMHR). A fair number of horses were registered with IMHR; back around the late '80's, after much 'discussion', IMHR was 'absorbed'by AMHA(the original AMHA circular logo looked odd because space had actually been 'reserved' for the word 'International' to be added,which would have made it the 'INTERNATIONAL AMERICAN MINIATURE HORSE ASSOCIATION' (what a mouthful!!)...but as I recall, a lawsuit stopped that happening, and there were some severe 'hard feelings'over it, because the agreement to do that was supposedly part of the reason notable IMHR backers had (reluctantly) agreed to the merger.
Margo