Possible Clues:

• Number of Super Bowls Dan Marino won
• 'Nothing, nothing about a letter up at last (4)'
• Much-repeated part of binary code
• Coke ___
• 'O, that's the end of 15 across (4)'
• Worthless person that has no effect, in addition
• 49-Across number, maybe
• Little Annie Rooney's dog
• It's less than one
• 'O, that's what it is (4)'