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.
No, the point you tried
and failed to make was that in "30+ years of published work" it never happened.
We proved it did. Repeatedly. Whether or not it was common is irrelevant. No, it isn't common. It doesn't have to be.
(Oh, and it will be exactly 30 years this May, the anniversary of
Darkwalker on Moonshae.)
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.
You're shifting the goalposts. How common is irrelevant. It happens. Your sudden interest in the "inconsistencies" is attempting to shift the tone of an argument you lost.
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?
The gods can. See Tyr. And the entire Mulhorandi and Untheric pantheons.
You still have not given a citation for your comment about Lolth. Where did Ed Greeenwood write or say this?
Given it's so contradictory, Ed could be misquoted or made a slip of the tongue. He could be suggesting it was a different aspect of the goddess. Or you could just be outright misremembering like with the Dragon articles.
(Very likely the Greenwood was actually referred to "Tiamat" and not Lolth, as Tiamat was part of the Untheric pantheon, based on the original Sumerian Tiamat. Gygax borrowed the name. Those were very different gods, although that has been retconned and now the Untheric Tiamat is the same as the regular D&D Tiamat. )
This crossover stuff was never fully played upon for some reason.
Likely because there was so very, very much Forgotten Realms to explore that you didn't need to crossover. The focus of the Forgotten Realms products was... the Forgotten Realms. Surprising I know.
Compare this to, oh, Spelljammer where the focus
was crossovers. And they devoted
an entire book to crossing over with the Realms:
http://forgottenrealms.wikia.com/wiki/Realmspace
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.
Yes.
Because the alternative is moving all the adventures to the Realms, which they have learned players/ fans did not like as much. So they're doing something to present the adventures in their traditional settings in response to feedback
and you're complaining about that.
They really cannot win.
Okay, they could have found an inn in Sigil to use. Or the much more appropriate World Serpent Inn. But the inn isn't really the focus of the product. It's a framing device. A title and some flavour text. Maybe we'll get a map of the inn, but we'll just as easily get no description. Even if they give the Inn a good two-and-a-half pages of text that's still only 1% of the total product. That's nothing. (And more than likely the Yawning Portal will just feature into a one or 1/2 page introduction like Volo in
Volo's Guide to Monsters.)
It might as well be "Tales from <Insert Name Here>".
I'm not going to fault them for finding a flimsy excuse to play up the most famous tavern in their lore.
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.
Well, we'll find out in the Yawning Portal book, won't we? They could explain it there pretty darn easily.
It'd be pretty easy to go from Sigil to Yawning Portal. Or the myriad spells that allow travel. And it's been LONG establish in the Realms that portals and gates are a thing and everywhere (as seen by the Imaskar going all Goa'uld and abducting humans from pre-history for slaves), so it'd be easy to have a portal in the tavern.
Or you travel through a portal from a dungeon in one world into Undermountain, surfacing in the Yawning Portal. Because it's been established their are planar gates in the ruins of Undermountain, as seen in
Undermountain: Stardock, the Sargauth Level, the Maze Level, the Terminus Level, and more.
It
is a bit of a retcon to the tone of the Yawning Portal. But no more than would be necessary to set it anywhere else, such as the Points of Light setting as you initially suggested, which has even less contact with other worlds. That setting just stole classic dungeons and places and used them to flesh out its backstory. But that runs into the problem WotC is trying to avoid: changing the setting of the classic adventures.