Artist Proofs are not usually meant to be out in the world. The small flaws, usually only things that the artist notices, make them not suitable for the numbered editions and in the "art world" the general thought is that selling them only undervalues the editioned prints. But as an artist, I know how much work I put into them and what's the point of packing them away so they are never being enjoyed? I'm also a consumer and I choose to think of APs as a way to offer a more affordable option of original art. 
 
Refer to the listing for the edition of American Redstarts for all the details. After all, this AP was created at the exact same time in the exact same way as the signed and numbered ones, it's just slightly .... flawed!