Adam’s Practical Bookbinding has an intriguing passage regarding knives to cut binders board:

Instead of sharpening the knife, the tip is broken off, exactly the same as modern Olfa type snap-off blades, except that there were no score lines to make the snap. The description of the knife makes it sound similar to a mill knife. I’m not sure why a broken edge would be sharper or hold the edge better when cutting something as abrasive as boards. Recently on the Book Arts Listserv there was a discussion about resharpening Olfa knives to save a few pennies. Could the original broken edge be superior?

Adam, Paul. Practical Bookbinding. London and New York: Scott, Greenwood and Co. and D. Van Nostrand Co., 1903. (p. 86)