Here's how MLB describes "Team Issued," as per their
website:
Team Issued is a designation by an independent third-party authenticator who attests that the item was issued by the Club to its clubhouse. This designation is not intended to determine use of the item in any capacity.
Basically, that means the team can put a brand new, unused jersey in a player's locker in the clubhouse, and even if the player never wears it, never even has any physical contact with it, it still qualifies as a team issued jersey.
(At least, that's how I interpret it.)