I'm not sure i'd entirely go for this. But I speak as someone with little general knowledge of Wonder Woman and the history of the Lasso, so I could be entirely wrong.
The way I see it, there's more than one level of knowledge and belief. I can think on the surface that i'm doing something for one reason, but it could actually be for another; I might know that and be consicously lying to myself, or not understand it consciously. And then there's just the actual truth, which may be different from both of these things. It could be the Lasso works within the total realm of knowledge and belief, not constrained by only surface considerations, but still constrained to within that person.
In the first example, Captain Nazi knows the things that are being showed, but is deliberately choosing not to think of them or confront them. The second's less clear - does Tom know that WW doesn't love him, but is trying not to think of it, does he honestly not realise it, or is this entirely new knowledge to him? I think it could be played all three of those ways.
I suppose the question to figure it out is this; what if the deepes secrets of someone's soul were also wrong? What if someone is honestly mistaken even on that level, and have repressed or ignored what they think is true? Would the Lasso reveal the deepest knowledge - the truth according to that person, which is not necessarily what they think on the surface - or the actual truth?