There are only so many ways to twist a string, and practical knots tend to be simple, knots get reinvented all the time before ending in a book. This is also why there there is no approximation in knox tying. If your knot is slightly different than what's on the book, it is probably another knot (see: square knot, granny knot, thief knot, grief knot), or just a mistake no one bothered to give it a name.