The question came up reading about the Om 31 in volume 3 of the Guterwagen series. A photo shows an Om 31 with zonenschriftung in 1957, with a '(!)' next to the date, indicating it was surprising to have the lettering so late. Thinking about it further, I was still a little more surprised that it would be applied to a car built 1953.

What I more or less have straight is that the DB was established in 1949, and that the zonenschriftung was to be removed by 1955. Apparently this interim was a period of anything goes, with all kinds of combinations of Ep. II and Ep. III lettering, even on the same car.

RK