As far as I have heard it entirely about provenance: a written record that describes how the object (in this case, the brain) was preserved and changed hands over the years. If you're asking, is there some way to tell from the physical brain itself, apparently not, except that it matches up with the description in the provenance. But if you're wondering, could Harvey have just grabbed someone elses' brain and then called it "Einstein's brain," faking the provenance — I don't see why not.