Mine is from the sixties. They still were then. I believe the target stocks on my 27-3 were. I would have to check to make sure. It is from the early eighties.
You have to remember, that person who was numbering grips is a human.
They eat lunch, go to the restroom and leave early. So a few stocks did not get numbered. Back then, nobody cared. The grips fit perfectly. There were no mod-28 collectors 50years ago.