There is a letter followed by numbers on a horse registration. What do the different letters, A, I, L, N, P, Q, T, U, and X stand for?

Explanation of Registration Numbers

All numbers for numbered American Quarter Horses

Letter A in front of number means Old Appendix Horse
Letter I in front of number means International Horse that traces back to American Quarter Horses
Letter L in front of number means Appaloosa Horse, also AP in last two positions of name
Letter N in front of number means National Quarter Horse Breeders Association
Letter P in front of number means Paint Horse, also PT in last two positions of name.
Letter Q in front of number means American Quarter Racing Association Horse
Letter T in front of number means Thoroughbred Horse, also year foaled in last two positions of name
Letter U in front of number means Unregistered Horse
Letter X in front of number means New Appendix Horse