The numbering of each print in any edition has significance only when the artist uses materials to transfer images to paper that don't hold-up well to repeated use. (A soft wood block, metal plate, or resist degrades slightly with each print made.) The first of these editions, (or the first prints to be made), are then known to have more detail and are considered better in quality and worth more.
     With modern day print-making methods, however, (such as with giclée and lithography), there are no noticeable differences between the first and last impression or print. The quality is the same from first to last. The numbering of prints made with these methods, therefore, would only have significance in a type of inventory control system for the artist and shouldn't impact the retail value of the print.

AP - Artist Proof or Épreuve d'Artiste. Also E.A.
BAT - Bon à Tirer Proof or "okay to print." Only one for any edition.
TP - Trial or review proof. Pulled to see what the print will look like at any stage of development. (Any number but usually very small.)