This is self evident from my perspective. We all believe what Griff and Co. present in the story, or we don't. I questioned his identity when I read these chapters because the characters in Westeros all seem to believe that the Mountain dashed his brains out before raping his mother.
"There is evidence for both theories, which I will not list exhaustively. But, for example, there are clues from Varys that suggest he genuinely believes that Baby Aegon is still alive (and he might well know, thanks to his little birds in King's Landing). On the other hand, there is the prophesy of the "mummer's dragon" and other indications that suggest that Young Griff might be an impostor."
True enough. GRRM does like to spread seeds of doubt when dealing with historical events.
"But what if there is truth to both sides of this question? What if Aegon survived and escaped King's Landing, but Young Griff is not that child?"
I struggle with this question based on a supposition. How did Aegon survive having his brains dashed out as an infant and who is Young Griff if he isn't the son of Griff or Rhaegar?
"I've seen the question asked: Does it matter if Young Griff is not the real Aegon? After all, he seems to have been raised to THINK he is Aegon. And he seems like he might be a semi-decent kid."
It matters to me because that would mean that all of Westeros, whom he has apparently been groomed to rule, believes that he is the real deal. Him not being the real deal would be a massive lie. Westerosi society is structured around inheritance and lines of succession, after all.
"In short, who cares about this whole "(f)Aegon" subplot, …. Unless, perhaps, there is also a real Aegon out there, who is, in truth, one of the 3 "Heads of the Dragon"; and perhaps even "The Prince that Was Promised". If there were, it might matter that an imposter is claiming the throne in his place."
See above. All of Westeros would care because they believe that the line of succession was broken when Gregor Clegane killed him.
"Are there any characters, to whom we have already been introduced with reasonable prominence, who might possibly be Baby Aegon?"
There are no characters in the books with smashed heads.
"Let's start with All the POV characters; then throw in for good measure, all characters who were important enough to receive at least a mention in the Appendix to the original "A Game of Thrones" volume. Could any of these characters be Baby Aegon? Go down the list one by one, and you're answer will be "nope", "nope", "nope". Wrong age. Wrong sex. Wrong appearance. I've seen Jon Snow mentioned in this capacity, on the theory that his age could possibly be wrong, and he might be older than he believes. But if so, where did he get his Stark features?"
I'm with you. None of these characters are likely to be Aegon VI Targaryen.
"I've seen only one character who might possibly fit the bill."
"Quentyn Martell. POV character, listed in AGoT Appendix. Right age. Right sex. Martell features which (if he is Baby Aegon) would be from his mother. Backstory involving fostering with the Yronwoods at age 3, providing an ideal circumstance for a baby-swap. He dreams of Fire and Blood. And the last thing we saw him do, before Rhaegal attacked him, was face down a dragon with ship in hand. And Viserion, at least, actually seemed to respond."
"And of course if (f)Quentyn is (r)Aegon, then (f)Aegon is probably (r)Quentyn. And that tells us who Septa Lemore is. She is (r)Quentyn's mom, Mellario of Norvos."
Okay, so Quentyn is not really Quentyn, he's Aegon. More wows! And that means that the Aegon that Tyrion encounters on Shy Maid is actually Quentyn? Wow, wow, wow! And, furthermore, Septa Lemore is actually Mellario of Norvos? Wow, wow, wow, and more wows!
"There is a theory that Quentyn is alive -- that due to one of GRRM's signature fake-outs, another (probably Prince Tatters) died in his place in Dany's bed. I believe the theory, but I won't describe the theory in full now. One of the objections to the theory has always been: "But, why does it matter if Quentyn is alive?" Well, here's your answer."
It matters that Quentyn is still alive because he is actually Aegon VI. Gotcha.
"Give me one good reason I should not believe that Quentyn "the Frog" Martell is the real Aegon."
The real infant Aegon had his brains dashed out on a wall by Gregor Clegane.
I will stop now. I admit that I don't have very strong feelings one way or another on your theory. I was just having a try at your posting style. You often take quotes from other posters who take the time to write responses in full paragraph form and then you break them down and respond to them one sentence at a time. I find it tedious to read this style of response, especially since your responses to each sentence tend to be longer than what the original poster stated, and I have noticed that a handful of other posters have adopted this approach lately. I have to say that I got even less enjoyment out of trying this style of response than I get when reading them. For one thing, it makes the response come across as more argumentative than maybe it needs to be. I'll be moving along now.