My understanding of the situation is that of the 3 types commonly seen, the 2 arm ones were pre-war. C-L were bombed and lost most of their patterns during the war and so developed the rather elegant round section 3 arm ones after the war. These developed a reputation for snapping, though I have never seen a broken one, and so they then produced the 3 arm rectangular section one until they went out of business. I think there may have been other patterns in the 20s and 30s, but these are not commonly seen.
Peter Brown, Lincolnshire, England.