To qualify, players have to have won at least three consecutive championships with the same team. This means that a player who was on-roster for two consecutive championships but NOT the third (even though a third championship to complete the three-peat happened the following year without the player) will NOT qualify.
In order to create a playlist on Sporcle, you need to verify the email address you used during registration. Go to your Sporcle Settings to finish the process.