Unless I'm missing something, there is an alternative solution to Puzzle 3310. The given solution is Rd1+ Ke2 Qh5+ Qf3 Qxf3#. But there is also Nd3+ (Qxd3 exd3+ Be3 Qe2#) Kd1 Nxb2+ Ke1 Rd1#.
to check whether you are missing something, you can play those positions against stockfish, then count the moves
I just came across this puzzle today and found the same lines. It gives Nd3+ as a failed move despite the fact that it leads to mate in the same number of turns as the main continuation. Local analysis confirms the lines that darken provided in the OP. As far as I can tell, the Nd3+ lines should be just as valid as the Rd1+ line.
Also, I'm just a little bit salty about those 28 rating points :(
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