What is a certificate of authenticity?

Answer 1

Certificate of Authenticity - Also known as COA - A statement of the genuineness of an item (often an autograph), printed on a piece of paper, thin cardboard, that is furnished to the buyer by the seller. Certificates of authenticity can be issued by the seller or a third party authentication service. The validity of the certificate of authenticity depends upon the integrity and knowledge of the seller or authentication service.

For more information on other Baseball collectible terms visit the link I left below "Glossary Of Baseball Collectible Terms"

Answer 2

no. However you can have most (not all) items appraised by a specialist who may be able in some cases to given a new certificate, it will be dated as a second certificate but is often better than nothing