Do you win if you get Yahtzee?
Your first Yahtzee is worth 50 points, and any additional Yahtzee is worth 100. You can win a game on that second Yahtzee alone. So by all means, if you roll five 6s and each slot is filled except for sixes, ignore the open slot and call it a Yahtzee.
As long as youve scored 50 in the YAHTZEE box, you get a YAHTZEE bonus for each additional YAHTZEE you roll - just squeeze in the check marks if necessary!
What is a great score in Yahtzee?
Since you only get 13 rolls in a game (see the rules, not all players realise that additional yatzees dont give you extra rolls) the high score ever possible is 1575 = 13 yahtzees including all full scores in all other boxes.