The only firm date on the first printed book

A priest in Mainz finished colouring in the capitals of his new Bible, bound it, and wrote the date at the back — which is the closest thing the Gutenberg Bible has to a birthday.

Nothing in the book says when it was printed or by whom. Heinrich Cremer's note in the Paris copy fixes the outside limit: the sheets had to exist before he could decorate them. Everything else about the date is inference from paper, lawsuits and a couple of letters.