Possible Clues:

• Numbers puzzle
• Kudos built on university logic puzzle
• It's puzzling to return most of the dust that's fine underground to begin with
• *Paper puzzle usually involving a 9x9 grid (2004)
• Game typically with 81 squares
• Variation of the Latin square puzzle
• You and me giving up on party for backward neighbours - the difficulty is getting the numbers right
• Numerical puzzle with a 9x9 grid
• Country lacking an adequate universal puzzle
• It's puzzling to return most of the dust that's fine and underground to begin with