I think you got it. It's hard to describe well, and probably just a reflection of my own mental limitations to call it "required guessing." There may be some methodical solution I am missing in any given instance. That's why it would be nice to know for sure if there is a solution. I usually struggle to see triplets in every instance, (where some combo of 3 numbers across 3 spaces in a group, result in locking the spaces to these 3 potential numbers). This is where it would be nice to know if all potential triplets are unsolvable.
Personally, I have a collection of around 100 hard puzzles on Open Sudoku that I have saved and usually just clear and replay. When I get to one I really can't seem to solve methodically, I do my best guess, finish the puzzle, and then delete it from my collection. Sometimes I forget to delete one or two. I just went into a small set I haven't played in awhile, grabbed one with a longer completion time, and solved it to what looks like deadlock after a few minutes of scanning for solutions. It already made it past my initial play and deletion regime, so there is a good chance this still has a triplet somewhere that I am not picking up on. If you have not played Open Sudoku, the notes can be automatically filled to all possible values. The second image shows the point where I would want to know if a triplet or even a quadruplet solution exists.
I think this is how it would need to be solved in code too; working up in methodical complexity until it is possible to check for trip's and quad's. It would be a lot of code to solve it this way. At least it would if my amateur self gave it a try.