Artist Proofs
All Limited editions have an over run of about 10% of the edition size. This is to cover for any damages to prints during the long process of gaining the driver signings which can involve shipping prints all over the world. Some prints have even been damaged during the actual signing. (no names mentioned). Once the full edition has been assigned a certificate and issue number, all remaining prints, normally 25-50 become what is called an Artist Proof. These have all been hand signed by the relevant personalities and differ only in the fact that they are not part of the numbered edition.
Many rare prints are only available as Artist Proofs, and offer an excellent alternative to buying a print on the secondary market where it would probably have already been framed and possibly even damaged.