Yeah, but these can definitely be used as complementary sources - with proper integration, they'd match almost always, but all mismatches seem like you should assume that the sign is there; e.g. if a sign is in map but not in DB, then it's likely the sign is obscured by something but still should be followed; and if there is a sign in vision but not in DB, then it's likely to be part of some temporary road works. The scenarios where the sign truly "isn't" there are possible, but comparably much more rare.