Voadam
Legend
From the 1e Forgotten Realms Boxed Set page 5:The first edition box set explicitly states the large-scale 1e/2e maps of Faerun are in-universe maps which might contain errors. I don't see any reason to assume later maps are any different. As far as I can tell, the only maps that are guaranteed to be accurate are the ones the DM has decided to use during an adventure you're playing.
Two of the maps are drawn to provide a general overview of the Realms, running from the Moonshae Isles in the west to the land of Thay in the east, and from the Spine of The World Mountains in the North to the Jungles of Chult in the south. These maps have been drawn with that information available to our representative in the Realms, Elminster the Sage, and represents what is known of those lands from the mindset of the Dalelands and Cormyr.
The other two maps are detailed blow-ups of sections of the former maps, covering that region from the Sword Coast to The Dragon Reach in great detail, for use in adventuring through the Realms. As more of the world is fully explored, more maps of this and scale will be made available for use in Realms-related products.
So it sounds like the Sword coast maps are supposed to be game accurate down to the hex level for exploring and traveling, while the bigger map is a general overview that is specifically based on in world knowledge from a certain perspective.