Here's what I have, Lagopus, from an article on Westley Richards by Colin Greenwood, Double Gun Journal Winter 2003:

"The marks ceased to be used from 1941, but were reintroduced for the calendar year 1950, this time with a circle divided into three . . . When this series expired in 1974, the circle was used without the inner divisions." If that's correct, then the mark for 1974 would have to be the new style--larger, and enclosed in a circle.