It took years grabbing these as they've popped up for decent prices, just recently grabbed V to finish it off. Wish III had been released as a GBA cart.
FFTA is one of two games I have ever 100%'d. Played that game so much back in the day. The reward for 100% is awesome, and I have very fond memories for that game.
It was many moons ago, but I recall this is correct. You had to place locations in a specific pattern for some of the mission items and it was totally possible to do with a single cart, just you basically needed a guide to figure out all the combinations to create the right map. It was not a trivial thing, and I recall using gamefaqs a lot.