: Many sudoku apps (e.g., Sudoku.com, BrainBashers, Puzzle Club) number their puzzles sequentially. "129" could simply be puzzle #129 in a collection. A player might be comparing it to another puzzle, saying puzzle 129 is "better" (e.g., more elegant, harder, or more logical).

They write every possible candidate into every cell. This creates visual static. In the 129 method, you should only write candidates after you have eliminated locked candidates and hidden pairs. Less ink means more clarity.

: Studies suggest that Sudoku can enhance short-term attentional capabilities and concentration.

Take a puzzle with pencil marks. Set a timer for 2 minutes. Remove as many candidates as possible using only naked/hidden pairs and box-line reduction.

: "129" might be shorthand for a variant where certain digits appear 129 times? No—digits 1-9 appear 9 times each in a standard grid, total 81 cells. 129 is irrelevant here unless it's a multi-grid or mega-sudoku (e.g., 16x16 has 256 cells; 129 is still not a round number).