You have to have the content for the signature to tell you anything. A digital signature only has meaning if it has been verified. Well, sort of. If you don't check the signature it tells you nothing. It's there if you need it.
Digital signature is just one of the pieces of information about the document.
It's there when you need it. The timestamp is a signature on a document. You are allowing these signatures to not be co-located with the content signed, which indicates that I may be misunderstanding your point of view. Actually this is what your timestamp is. OK, I think we are in different contexts here.