Vor 7 Stunden
If I understand the rules correctly, gold cells are a special case of Pencilmark Sudoku (here is an example). Basically, each gold cell has up to three candidates; if every gold cell is given, then each non-gold cell has 6-8 possible candidates.
About box 5 in the linked puzzle, there is nothing obviously wrong, the three gold cells have candidates 56, 568, 69. Note that the third candidate is not "number of the box it is in", but "position within its box".
About box 5 in the linked puzzle, there is nothing obviously wrong, the three gold cells have candidates 56, 568, 69. Note that the third candidate is not "number of the box it is in", but "position within its box".