How do you know if a baseball card is rare or not?

Rarity is RelevantAt one time the T-206 Honus Wagner Baseball card was considered to be the rarest baseball card with a population of about three. There are now about 75 -100 known example of the card. There are at least 7 other cards known to be more rare. There are three known examples of the 1921 Frederick Foto Babe Ruth card. Cards like this a rare, and you will find article written about them as they surface and come up for auction.

Pre war tobacco cards, older cards from the 1950's, and 1960's are rare because they were printed in fewer numbers, and lost to time as many were thrown out or ruined. Traditionally, manufacturers would produce cards in several series. The High number cards, the last, or near the last series of baseball cards issued from the set are rare as relevant to the rest of the set. As the season would wind down, so would public interest and production. This lower print run resulted in a more limited supply, and later, more valuable cards.

Newer cards are over produced. Rarity would be relevant to the demand for the card, and the number of cards available on the market. Cards in high demand regardless of their print run become rare as more collectors purchase them. Typically these cards will have a higher value as they become rare on the market, with higher demand.

Price guides will make a notation as to sets that are printed in limited numbers. "Rare cards" that are printed in fewer numbers as relevant to the rest of the set receive the notation "SP" in price guides.The notation SP means Short Print, a card that was printed in lesser quantity compared to the other cards in the same series.