From what I remember, the basis for the argument came from the Nixon pardon, and the Carter administration getting pressure to take Nixon to court because the pardon didn't carry any force. Pardons without charges are very rare, and I had understood that's because nobody wants to deal with exactly this - that the pardon would carry all the legal force of a polite request, so it relies on continued DoJ cooperation.
I'm also vaguely remembering something about a supreme court case that said overly-broad pardons are invalid, but that may have been in regards to pardoning future crimes.
Anyways, I'm out of my wheelhouse, and this isn't really important anyways. Can we just call this an open question?