I think some puzzles require a specific amount of solved puzzles is a very nice idea. That can probably be one of the hardest levels in the game, so players are prepared for that. It would be a good storytelling device that hides the final revelation too. Think of how Return of the Obra dinn hides the final and most important part of the story behind a 100% clear (I am not going to spoil it in case you haven't played it, you should though :) ), and that makes the game super satisfying.