I'm admittedly a small fry, so my dollars will never be put to the test on the really big books, but I do wonder if you're not correct about all this, and, as you say: never say never.
If you can shift the nicks on the spine around to the back cover by disassembling and pressing the whole book, then why in principal can you not trim off the resulting 1/32 of an inch or so of page reveal upon reassembly to have a square edge again?
I mean, it's all about how it presents in the slab after all and that all important number at the top...