AoL came out three years after LoZ, so anything can happen in three years.
Nope. LoZ came out on February 21, 1986 and AoL came out on January 14, 1987 . . . that would mean that they came up with and designed and finished the game in less than a year...
And yeah, there hasn't been explicit mention of a fourth piece, but there's enough evidence for and against a fourth piece to make the fate of a fourth piece a bit uncertain.
That's a fallacy. Simply because there is no evidence for something absurd to NOT exist doesn't mean that it probably does. That would be like me saying, "Well, there's no evidence that a Flying Spaghetti Monster created the world, but there's just as much proof it did as there is it didn't, so it probably did."
We won't really know for sure until Nintendo actually says something for or against the argument, which may or may not happen,
That's not going to happen. Because it will never occur to them to clarify something that is obvious already. There is no fourth piece. It would never occur to them that anyone would ever think there would be, so they will never state there is or isn't.
That's something Miyamoto and Nintendo love for us to do with this series, though--come up with our own theories and debate them. That's one of the true natures of the Zelda series.
Um, again: what? I've never read anywhere that Miyamoto or Aounama "love" for us to come with theories. Neither of them have mentioned any such thing. It has NOTHING to do with the "true nature of the Zelda series" . . . No offense, but where do you get this garbage?
Again, it's CLEAR there are only three pieces. We see the birth of the Triforce in drawing in ALttP's instruction booklett. Three pieces. We see the birth of the Trifoce in OoT. Three pieces. We see the birth of the Triforce in TP. Three pieces.
It has three pieces.