Posted By:
Steve M."Rookie" to me is the first card of a player after or at the time he became a major league player. Minor league depictions are not "rookie". Ideally the card should depict the player in a major league uniform.
Players depicted, singly, on a postcard are cards. Team postcards are not. So, PC796 Sepia would be a card. Pinkertons are cards. W601 Sporting Life is not a card. Supplements, whether single player or not, are not a card.
A more satisfactory way for me to collect, if I were so inclined, would be "first" card rather than "rookie" cards.