Good frontsite content if we can get some solid proof.

What treasures turn into other items if you wait until further in the game to open them up? Off the top of my head I can only think of the Rune Edge in the Moogle's Cave eventually turning into the Drainer, and whatever the hell in the cave to South Figaro that turns into a Thunder Rod and eventually a Ribbon if you don't open it until the World of Ruin.

Anything else come to mind?