Something doesn't sound right to me either. Without the ridge on the inside of the keeper, what's going to keep it from coming off the end of the valve? It's been awhile since I've had one of those down but i'm thinking they had the ridge. Is there any sign that there was a ridge and its worn down?
I'll have to give them a closer look next time I get a few moments. That will be a couple of days the way this week is going. I've never seen these without the ridge but I just thought it was the way briggs made them.