The original pressings of the album had a top opening sleeve - ie the record opening was in the top of the sleeve, not the side. These were individually numbered and had "The Beatles" in embossed letters.
Later copies, from about the mid Seventies onward, lost the number and had the regular side opening sleeves.
What Kat is referring to is the matrix number in the run-out groove - this is stamped onto the record from the master plate. Any alterations to this number on the run-out would have been made to the master and stamped on all subsequent pressings rather than amending each record individually.