This category is for PM clarinets without model designations. Information from Gary Kern:
“There are posters from 1941 (see http://penzelmuellerfanclub.com/posters.php) of Jimmy Dorsey and Woody Herman with Artists, so probably the Artist (and therefore model names) was introduced sometime in the 30s. Their bands were big in the 30s and 40s.
One pre-WWI reference was sn/339 PM with the wraparound register key and rollers. It did not have a model designation either.”