The Pokemon Base Set is the name given to the first set of Pokemon cards. The Base Set was released in January of 1999, three years after the Japanese version was released. The set contains 102 cards… highly sought after by collectors who want the first appearance (sort of like a Rookie Card) of each Pokemon. There were several different print runs of the Base Set, some being more valuable than others.
1st Edition cards are more valuable, they’ll have a mark below the character window that says, “1st Edition”. If the card doesn’t have the mark then it’s part of the Shadowless, Unlimited, or dated Unlimited editions.
The Shadowless print run does not contain a drop-shadow around the character window, and they’re missing the 1st Edition mark.
Unlimited Edition cards are the most abundant of all the editions. They’re still valuable as a Base Set card… but not as valuable as the 1st Edition or Shadowless cards. Unlimited cards will have a drop-shadow around the character window. In the second print run of Unlimited Edition they added the copyright date “1999-2000”.
