EzekielRaiden
Follower of the Way
Not at all. There are enormous swathes of FR that are barely detailed at all, and huge chunks of it can be significantly massaged into more or less whatever the GM wants. Maztica, for example. It was zorped over to Abeir during the Spellplague, and came back after the Second Sundering. It literally spent a hundred years in a completely different world, one bound by different rules and very much not like Toril. That is a golden opportunity for any GM to do basically whatever they want, because you can just say that it was some not-previously-known weirdness of Abeir that now has found its way to Toril.If I go and pick up the latest version of Forgotten Realms and run a game in that, far more than 95% of the setting has been nailed down before ever encountering a player.
And that's saying nothing about any of the other like seven multiplanar catastrophes and upheavals that have rocked FR over the centuries. At this point, for having so much of Toril allegedly mapped and catalogued, there's an absolutely ENORMOUS space of "well...we don't really know!" to work with.
A GM who declines to do so is not in any way specially respecting the written story of FR. They're just saying they don't feel like going to the incredibly token effort of saying "oh, things like that now live no Maztica because of the time it spent on Abeir, so they're very rare in the wider world but not impossible" or the like.

