I disagree with your theory. I have consistently gotten non-rare collectibles, or even none at all. I am getting so angry that I am about to uninstall the game. I have two simultaneous villages that I am working on, one is nature faction, the other magic. I have completed all of the puzzles, but when it comes to the chief pointing out collectibles, he/she often points out nothing at all. I have tried pausing the game, and thoroughly searching the entire map, but come back with nothing.
Weasel, I know it can be frustrating not to find missing collectibles. That happened to me too and there were more times the Chief pointed out nothing than he pointed out a rare collectible. I was just missing about four. I kept searching and within a few days I was just down to missing one. It took me almost two weeks to get that one and the Chief finally came through for me on that one. If you uninstall the game, you'll lose all your hard work solving the puzzles and your little villagers.