So in other words, I should place my campaign and adventures in...
The Serpent Hills (east of the High Moor)
The Wood of Sharp Teeth
The Desertedge Mountains (outside the Dales), and
The Nation of Sembia
These will not have any modules or sourcebooks set in them, and are left solely for the DM to develop, without fear of contradiction or invalidation.
...Right?
-O
Or maybe in one of the small settlements in the Western Heartlands (there are many small settlements there)? Or in the Vast? Or the Border Kingdoms, which have been detailed in 'Power of Faerun' and as free articled on the WoTC site? Those are just quick examples, and there are even whole continents that have not been touched in official Realmslore, if you want to be creative.
I'm not sure why people persist that this is solely a FR-related issue; as I mentioned, I'm sure Eberron veterans would gripe about my lack of canon lore. If you're expecting to make major changes (such as replacing a city or a while kingdom with your own version, or blowing something up, or introducing new deities), I'm quite sure you'd have a problem with fans of *ANY* setting. Even if you're only using a single campaign book, and running the game for a group with similar exposure to official lore, I doubt it would any different if you decide to run your campaign in the same place their previous DM ran several campaigns in -- unless they're not interested in any names or places or maps, you'll likely bump into this very same issue sooner or later ("But I thought it was Lord Blackhand who ruled here? That's what the previous DM said, and there should be no wizards or clerics in this town! And the inn was called 'Majestic Magic-user'!").
I usually try to discuss this with the players, if I don't know them; especially if I'm running my first campaign in a setting (and I usually go for small and remote border settlements). Talking usually always helps, just as it helps to communicate which sort of campaign I want to run and which sort of campaign and with which sort of characters they want to play in.
As I said, not all changes are "bad". At the moment I'm playing in a heavily-modified AoW adventure path set in FR; it's so different (even from the FR conversion notes) and it's hard to recognise. And the DM has made many major changes to canon lore to make it all better fit the campaign (including huge revisions to the history of the Savage Frontier, Netheril and major religions). And it *does* fit the campaign backstory so much better than official lore (and as another DM myself, I'm aware of the number and scope of changes), which is why I don't mind it at all; I might not endorse those changes as the "new lore" in my own campaigns, but they fit that one perfectly. In my Pathfinder playtest campaign I replaced an official town map with the Fallcrest map from the WoTC site, and everyone is okay with that, because the original is... well, I guess it's okay if you're into TSR-era CRPG city maps. Likewise, I wanted to use Kaorti and other Far Realm-related monsters there, so I rewrote centuries of official history for the kingdom.
What I'm trying to say is that it's always best to discuss which sort of "expertise" the players have on the setting, and where they may have played. Then, do some research on the area from those sources you have available, and pick what you like and modify/write the rest. That way you avoid a lot of the issues with players who have more knowledge and experience about the setting (or, at least certain areas) than you do. What do they want? Do they regularly take notes, and enjoy details? How do you prefer to run your games, and how much do you generally use descriptions or drop names? And so on.
