A lot of the footage that ended up in the Smithee cut was presumebly going to be part of the original verion that Lynch wanted to make, as he was supposidly shooting for somewhere above the 180 min mark length-wise, but the studio made him edit it down to what became the theatrical release. No way to tell really, as the Smithee cut is about that length anyway, and length is about the only way we could have told as a Smithee rough cut could include any footage a Lynch rough cut could. As a stretch off the top of my head means of possibly determining it's origin, do you remember if a male voice or a female voice did the opening narration (assuming that there was an opening narration at all that is)?