Remathilis
Legend
The point I am trying to make is that if you sift through 30+ years of published work you will occasionally find references of this and it is rare indeed. If this was such a common thing then we would have seen more crossovers in products and novels through all those years. There is TONS of inconsistencies in a lot of it. Mortals can pass between these worlds and yet the gods cannot? There were two Lolths and yet they were considered two separate entities that had nothing to do with each other?
For what its worth, Planescape states there is one Lolth, and her domain "touches every plane where she is worshiped.". (On Hallowed Ground). There is certainly some inconsistencies between how Oerth and Faerun has treated her, but overall Lolth is Lloth.
And some deities DO cross over: Tyr, Tyche, Loviatar, Silvanus, and Mielikki and Oghma all came from other worlds (Finns, Greeks, Norse, and Celts) to become Faerunian powers, as did all the Multhorand (Egyptian) pantheon. Mystara has Thor, Odin and a few other Norse deities masquerading as Immortals as well. The racial pantheons of the elves, dwarves, gnomes, halflings, and monstrous powers are shared among Oerth and Faerun (and a few other worlds), Bane was worshiped in a few domains of Ravenloft (due to importing of faith, Lathandar (as the Morninglord) Osiris, Isis, and Set (Egypt) and Belenus (Celts) are worshpped there too). Even Eberron insinuates that the racial pantheons were once worshiped before the Sovereign Host swallowed them up.
This crossover stuff was never fully played upon for some reason. From the looks of this new Yawning Portal product, it looks as if they are making the Realms into this Sigil like place where all these modules are suddenly common place and that people jump back and forth from Toril to Oerth and beyond.
No, they're saying the STORIES of these places have filtered across the multiverse. One DM could say "In my game, the Tomb of Horrors is a legend on a world far removed from Faerun" and another says "Well, in my game, its right next to Myth Drannor!" and the book doesn't say either is wrong; it just says the legend of the Tomb exists and if there is any adventurer stupid enough to try and find it, these are its rules." The book has an Appendix (like PotA did) for putting it whereever you like!
That's a sight better than "It now exists only on Nerath".
I could maybe understand if Wizards wrote up this article about something happening in the Realms that suddenly made all these other places accessible to most but they didn't. Now Teleport with Error allowed you to teleport to other planes of existence but that would be like the Plane of Shadow or the like.
The rumored Acerack-based adventure hinted at in The Hero and Dungeonology might address this. Or it might not. They may leave it up to the DM.
From Wikipedia: Like the Planescape setting, Spelljammer unifies most of the other AD&D settings and provides a canonical method for allowing characters from one setting (such as Dragonlance) to travel to another (such as the Forgotten Realms). However, unlike Planescape it keeps all of the action on the Prime Material Plane and uses the crystal spheres, and the "phlogiston" between them, to form natural barriers between otherwise incompatible settings.
From the Tome of Magic (2e): Although initially discovered and researched on Toril, the FORGOTTEN REALMS@ campaign world, the art of wild magic has quickly spread to other places. Wild mages, through teleporting, spelljamming, planar hopping, and even walking, have carried the precepts of wild magic to lands and worlds far removed from Toril.
Just too many inconsistencies.
You think this is bad: try making sense of the Doctor Who timeline!