It was common enough. I once bought a book I wished to read (mid-19th century) that had uncut pages. I asked a friend who is an antiquarian book dealer if the book was worth more unopened, and he assured me that it would sell for the same price in either state. Come to think of it, I bought some books a decade back or so from Ireland (some printed as late as the '70s/'80s, that were unopened. It's not just the top edge which needs to be cut, but also the front edge (opposite the spine). This is a by-product of how books are printed on large pieces of paper which are then folded (called signatures or gatherings). The signatures are sewn and assembled into a book. Most books are then trimmed before being bound.

Ceci n'est pas un seing.