In my first play we put them in the box and ran through the ones that were left over from set up. We ultimately ran out of those and then mixed up the one from the box to populate new tiles. Not sure if that is the correct way to do it, though.
Can you run out?
A two player is fixed at 25 tiles
A 3 player game uses 10 at game start then adds 20 tiles (4 Growths each add 5 tiles) so a total of 30 tiles
A 4 player game uses 10 at game start then adds 18 tiles (3 Growths each adding 6 tiles) so a total of 28 tiles
The game has 30 2nd play tokens, so there should be exactly enough for a 3 player game, and more for the 2 and 4 player game.
I've only played the game once so far, we discarded the unclaimed tiles.