dorkster, you are making it too complicated. Each round you must pick players with the same first letter of their last name and not a letter you have used previously.
If
round 1 you pick Babe Ruth, in round two you couldn't pick a player whose last name started with "R", but the other 25 letters are in play. If in round 2 you picked Simmons and Sisler, in round 3 you couldn't use "R" or "S", but any of the other 24 letters.
Hope this helps.