If you've tried the smaller 6x6 Product Frame Sudoku on page 33 of issue 21 you should note that the instructions are for the 9x9 version. For the 6x6 puzzle they should say "Values outside the grid reveal the product of the cells up until the first bold line in the adjacent row or column". In other words, they are the product of the first 2 cells vertically and first 3 cells horizontally in the 6x6 puzzles.
I'm uploading an updated PDF to clarify this for future downloads. Luckily in the puzzles I published it's immediately obvious it can't be a product of 3 cells in either puzzle vertically.
