I appreciate your sharing this kind of info, EC, because it's really hard to come by and decisions have to be made.

No, other than TOBG had become a massive bestseller, and prior to that PG had been a strong midlist author or perhaps on the bottom rung of bestsellerdom, nothing like now. With my publishers it was coming to crunch time. Sales were slowly increasing but not to the extent they'd like. Offer a new contract or drop the author? What to do? Shadows and Strongholds had come out in UK hardcover (different traditional cover) and hadn't exactly set the world alight. At the London Bookfair, people were passing it by. So they went for a last ditch attempt and changed the cover style for the paperback and brought in the head turned away, top of head missing paperback cover with the beautiful red-gold dress. Suddenly everyone wanted it. Tesco's supermarket took a huge order, sold out and ordered more. All the book chains wanted it. All the foreign publishers who had passed by the hard cover jacket, now wanted a piece of the action. And it sold steadily and strongly after that first surge. The Greatest Knight followed and walloped the ball out of the field. Now, I know I had been gradually improving my craft as a writer, but not to the extent of the sudden whoosh in sales. It was the covers that were appealing to the booksellers and the book buyers in the mainstream.
I do think that there are good headless covers and bad ones - some really bad ones, and I've been a victim of both. Also they've become a lot more old hat since those days, but they're still recognised as a brand form.
I find book covers and what appeals very fascinating!