Lovely mess, isn't it? I used a book's original cover boards for a rebinding in leather. I had assumed the covers were the right size because, after all, they were the originals. But no: they were 1/8" narrower than the pages. The covers had been cut so skimpy that the heavy cotton back liner I used added too much bulk and the pages protruded beyond the covers. By the time I discovered this, I'd already covered the boards in full leather and had no inclination to waste them. So, I pulled off the new sewn endpapers and the extra back liner. I peeled away paper layers from the flex-board spine. I lifted the pasted leather headcaps and back-cornered the spine edges. I swapped out thinner mull. Finally, I trimmed 1/8" from the foredges, which fortunately had wide margins. (I triple-checked the spine width, so that the text block wouldn't gape when everything was cased back in.) I felt guilty about trimming, but it had to be done. This one time. The book looks good and none the worse for wear. I won't show photos of the completed work until after I hand it to the person, because it's a surprise gift.