[aisrael]

(author here) That's a good question, I should've explained it better.

Technically, the other property of a puzzle is that there's exactly one good move. If you have one move that can mate in 3 and another move that can mate in 4, it's actually not a puzzle by the strict definition of the term. So, the reason I set the depth to 10 was because I'm actually looking for the second best move to be bad/losing.

For real positions, 10 might honestly be too low to confidentially state that every other move is bad, but for mate in 3 it was a good enough and still performed well.

[janalsncm]

At high enough depth the only real evaluations are #N, #-N, and 0. I’ve let stockfish sit on positions for an hour on my computer and it’ll find mate in 40. Of course in practical terms that’s computationally infeasible for your problem.