Why do chess puzzles need a unique solution? This is different from real games, where such situations do occur, but more frequently, there are multiple avenues to success. Contrary to what one might think, that makes chess puzzles easier, not harder! I have solved countless puzzles only because I knew that there is one and only one solution and therefore could exclude moves that I would have needed to consider in a real game.
Especially in some cases, where there are multiple different mates, all solutions should be accepted. Adding such puzzles in a set would lead to better and more realistic training. Also, practical positions may be added where the task may be to play until a certain evaluation threshold is reached or held for a certain number of moves against an engine. Why is tactical training today so "unrealistic"?