That's a failure of reading comprehension! I didn't say that Corypheus was the only unreliable source. Get over yourself.
Again, I don't think you understand what lying actually is. If you believe that it is "failure to fully disclose every possible fact at one's disposal and be a metaphorical open book to other people in relatively casual conversation", then you have a different understanding of lying than pretty much everybody who speaks or reads the English language. Similarly, emotional overreaction to trauma and an inability to be completely logical about serious events isn't automatically a lie either.
Aspects of Corypheus' story are indeed possible to corroborate, after a fashion. There's a reasonable consensus that Corypheus was a tainted being that was once a Tevinter magister; there is a probable identification of him as Sethius, of House Amladris. Both of these things have appeared in Inquisition and WoT 2, loosely classified as likely but not certain. The fact that Corypheus was tainted but not exactly the same as other darkspawn emissaries, combined with his extensive knowledge of ancient Tevinter, makes it likely that he participated in the attempt to reach the Golden/Black City. But, assuming that that happened, there is not a single shred of positive proof, aside from Corypheus' own claims, that he ever actually got there. Nor is there proof corroborating his claim that the city was empty (or that there was a throne in the city and it was empty, depending on how you read that particular line of his).
It is impossible to falsify Corypheus' claims because there is no possible way to come up with any evidence to refute it. Similarly, there is no possible way to come up with any evidence to positively corroborate it.
This is simply the nature of the problem: no one else was there. I don't have any particular bias against Corypheus, nor do I have any particular leaning toward Andrastianism or any other Thedosian religious tradition you care to name, but you have to understand what you don't understand. We can't take Corypheus at face value about the orb or the Fade any more than we could take the Guardian of the Temple of Sacred Ashes at face value about Andraste.
In fact, the game itself drives home the problem of autopsy to the player by using the Inquisitor's own experience. Did the player encounter Andraste in the Fade, or not? What exactly was that spirit-Justinia anyway? Was it Justinia herself or the spirit who helped the player escape the first time? What about the second time? None of this is made particularly clear. Whatever the player decides is the correct answer, and how passionately the character believes in it, is up to the player. The game certainly doesn't provide a clear answer.
I like that dance you have, it's sort of like mental gymnastics. You're doing more leg work to omit Corypheus than to consider it true. You keep using words like 'likely', 'reasonable consensus', my favorite being 'aspects' of support for your version of what is acceptable. Either you are running for some kind of political office or have made some sort of personal consensus of your own and reached a level of talking points memo that is burning up the note pad.
1) Don't suggest someone has a lack of reading comprehension because they make a suggestion you don't like.
2) Ignoring facts from one side to further the side you favor is a bias.
3) Yes. In the adult world, an omission of the whole truth is a lie, especially in a court of law.
Establishing that Corypheus existed in the real world via public record or familiar accord is proof. The wardens held Cory for years because of what he is. Their accord, Cory's accord and all of the investigating the entire game puts into finding out who he is justifies his claims too. We have no reason to believe that his account is false. Cory did not lie about anything. Except aggrandizing what he could do! The entire game we say, "so what! Cory, you are the big bad and the big bad is always wrong."
You're defeating your own argument with this line; Whatever the player decides is the correct answer, and how passionately the character believes in it, is up to the player. The game certainly doesn't provide a clear answer.
You are entitled to your own deduction. As am I. I say that excluding Cory is one of clear bias. You don't have to agree.
As for black city proof-somehow Cory got tainted real good. Somehow Cory gained the power to compete alongside the Archdemon in a body jumping contest. Somehow corroboration is left open for Cory even though he has nothing to gain by lying about it. If anything it cost him his God, Dumat, by proving the deity false or dead. Losing his God loses his authority and devalues him in his own society. Cory gains nothing from the truth here. If anything it drives him to become what he sought.
But let's say an apostate elf claims divinity by seeking other's power while lying the entire game and we suddenly must believe him. Somewhere there is a bias. The guy painting his own truths everywhere is his own citation. No bias there. Nope. But if we listen to the history of Fen'Heral, Dread Wolf; we know what history says of him. He makes Hissrad seem like a metaphor with a question mark. Is a lie by any other name; still a lie?
Now I have gotten over myself.