Did he invent a bit or a lot?

Currently we don't know and so we don't really know the scale of the deception.

For what it's worth I saw him a couple of times and thought he was brilliant but that means nothing in this context, as most of us who saw him think so as well.

What we want is the truth about which songs were mostly his passed of as something else.

We are talking about folk song and folk culture. This is an aspect of our culture in which people have a habit of saying all sorts of things with out much evidence!