Okay let's say PC #1 tells NPC #1,2,5,6,9,10 that x=y
PC #2 tells NPC 1,2,5,6,9,10 that x=z
PC #3 corroborates the PC #1 info with NPC #2,3,4,5,9,10 and refutes the info with NPC 1,6
but PC#4 informs NPC #1,2,3,4,5,6,7,8,9,10 that x=y=z
You would have to link the 3 pieces of (mis) information to each NPC cross referenced with the individual PC's information and maintain an accurate record over multiple information snippets. Confused yep me to. But over multiple campaigns with multiple players his kind of situation does occur!
I'm going to start with your last comment. So these multiple campaigns will all be impacting each other? Most people I'm aware of "instance" their worlds, so that the actions of Party #1 have zero impact on the world for Party #2. Your final sentence here implies that you run things differently, and I need to make sure I'm understanding properly.
The database structure necessary to model the scenario you've outlined here would need to track both who knows what *and* who told what information to whom. That latter component adds a significant level of complication to things, and it's not nearly as common a situation as the former. We've only designed things at this point to handle the former. We could do the latter, but it will take more work and is outside the scope of what we'll be providing in the initial launch and the first few updates after that.
As I mentioned above, we could potentially extend the "who knows what" mechanism to encompass NPCs, but that will not address the separate issue of "who told them what". We can definitely put this on the todo list, but it's not something to expect soon.