Well, you could say that about a lot of EU... but I meant that it's not officially part of the new canon.
Also, possibly TFA? Do you mean to say there was something specific in TFA that you think might have been a TOR reference?
The point is that regardless of it's source, it's still referred to as being the *actual* seal of the Old Republic by official sources. That it also came from a game (that probably isn't canon in and of itself) called "The Old Republic" just sort of hammers the point home.
You'd have to be a special kind of obtuse to dispute the intent behind using that design, in that context.
The problem with the Jedi being considered a "myth" is that the Emperor mentions being attacked by them when he addressed the Senate to officially declare the Republic's transition to the Empire. Something like that was likely recorded for posterity and is therefore definitive proof in the Empire's official records the Jedi did indeed exist. That there could be anyone who thought the Jedi to be a myth seems as silly as someone believing the Confederacy to be a myth despite hearing the Gettysburg Address.
Records can be altered. History can be re-written, especially in a totalitarian state. Just take a look at Joseph Stalin's photo album some day. Indeed, the speech itself was already re-writing history, who's to say that was the final version? Also, never underestimate people's capacity to believe fiction or disbelieve reality. Most people believe whatever they want to believe, regardless of empirical evidence.
Regardless, the point remains that this is Rey we're talking about. She didn't exactly have access to a Republic library. She presumably grew up on stories of what happened. Some of them probably massively exaggerated, others probably pure fiction. It's no wonder she'd think some of it was more myth than reality. Like for instance the one about the reborn Jedi chosen one that could make battlestations explode with his mind and defeated a million stormtroopers with one hand and was seven feet tall and shot lighting out of his eyes and...well, you see where I'm going with this...
She probably heard a lot of stories about Luke. Some of them probably true and accurate, others probably not so much.
Also remember that this is now two generations since the Jedi were wiped out. They're no longer in living memory for most people.
In ANH, yes, that's how it was depicted. But in TFA he actually does say he once doubted the existence of the Jedi.
IIRC the wording of that scene is: -
REY: The Jedi were real?
HAN: I used to wonder about that myself. Thought it was a bunch of mumbo jumbo. A magical power holding together good and evil, the dark side and the light...
Wondering about something is one thing. Outright disbelief is another. Also, he's clearly talking more about the existence of the force, not whether or not there used to be an order of laser sword waving crazy wizards that used "simple tricks and nonsense."