This arrangement in some extant copies has been altered by modern binders, who have divided the sheets, mounted each leaf on a guard, and then gathered them, at their own will, into quires.
"Fine Books"
Alfred W. Pollard
Hitherto the quires had been marked by hand, and this improvement was not suffered to drop for a time like the others, but quickly spread all over Europe.
"Fine Books"
Alfred W. Pollard
But the system of gathering from two to five or more sheets together into quires was practically universal both before and after the invention of printing, and this for the excellent reason that it reduced the quantity of sewing necessary in binding a book, and reduced also the risk of the sewing cutting through the paper or vellum, as it would be very likely to do if there were only a single thickness to resist it.
"Fine Books"
Alfred W. Pollard