I recently came across a logical method I had not seen before and have not seen again. It might be seen as a "cheat" by some but I was pleased to find it. A partial diagram of the situation:
X X X X X X
X X 23 23 239 X
X X 23 23 X X
I realized the 9 could NOT be in the place it was posited. The puzzle would not be solvable if the 2 or 3 were not in that cell (the 239 cell).
This depends on whether the puzzle is solvable, which I assumed, as we do, that it was. The puzzle was solvable by more normal methods also.