How Did Engravers At Babn In 1980 Make Changes To An Engraved Cylinder?

Working on a project and in need of expert help. In 1979 to 1981 small vending booklets were printed by BABN in Canada. There seems to be a series of changes made to the engraving cylinder. There were 72 booklet panes on the cylinder and the cutting guide on the tab (selvedge/selvage) was originally made of horizontal lines then changed to diagonal lines then changed again to horizontal lines. The rest of the cylinder was untouched. The flaws on the rest of that cylinder did not change so it was not a wholesale change. Any thoughts from those in the know?