For Harper & Bros. we have "...This code was discontinued after 1949. However, from 1922 to the 1970's, the words 'First Edition' should appeared on the copyright page. A number system that includes the year designation has been used since 1975.", see
http://www.whiteunicornbooks.com/home/glfirsted.htmlfor example. So it looks like it should say 'First Edition' if it is since the First appears to be 1954, see
http://www.worldcat.org/oclc/538974/editions?editionsView=true&referer=br