[Captain Kal]

In one of the Hitchhiker's Guide to the Galaxy books, a character gets an overdose of a truth serum. So, when he's told to tell the truth, the whole truth, and nothing but the truth, he proceeds to do exactly that. He tells all the secrets and truths of the universe from the dawn of time to its end.

While that was meant for humourous effect, it does have some bearing on the lasso's magic.

I honestly don't think the lasso could make someone know or do something that's normally unknown to them or beyond their abilities. If someone believes something to be so, even if it's wrong, the lasso wouldn't make them suddenly discover the real truth.

I think this is supported by the time the lasso broke under the influence of two equally valid truths that depended on the POV of the person.

Similarly, the old Magnus robot fighter comics had the hero's body and mind reformed so he could infiltrate an enemy stronghold. In his own mind, he no longer was Magnus and he truly believed he was someone else with that fictional history. Would the lasso be able to make altered-Magnus tell the truth about his own covert operations when he himself was unable to remember them?