My 914000 Ithaca has the serrated MSH. I doubt that you will see many examples with the checkered MSH past the 900K range. That being said, it would be perfectly feasable for a checkered MSH to show up here and there during later production. I just cannot see a change notice ( government approval to switch to the less expensive and labor intensive serrated parts) coming down and the supervision at Ithaca saying "Out with all of the checkered parts!" It has been well documented how many problems Ithaca experienced with production and, since the checkered parts were within spec., they probably used them until they ran out.