If you are a noble that has an audience with the monarch, how certain can the court be of your identity? Did nobility carry papers that proved who they are and not some random guy with fancy clothing? How about the court of law? How can the prosecution know for certain the identity of the person that stands accused?
There is certainly more to say about the specifics of your question, but you might find it helpful to review an earlier answer I gave here a few months ago that looked at the other side of the problem – how easy it was for people in this period to adopt a new identity. The answer is "Surprisingly difficult, in fact", for reasons that have quite a bit of bearing on the query that you're posing:
Did surviving servants steal their dead employers’ identities after the Black Death?