Here is yet another abnormal Pileated report. There's a lot more about abnormal Pileateds here.
I think the Cornell team ignored a basic point: nowadays, any bird that looks like a Pileated but has "too much" white on the wings or back is vastly more likely to be a Pileated than an Ivory-bill.
In all of "The Grail Bird", I don't see any mention of abnormal Pileateds, which to me is a shocking omission. (In fact, I used Amazon's "Search Inside the Book", and I find no occurrences of "abnormal", "leucistic" or "aberrant" anywhere in that book).