Sheaffer was known to be very aggressive regarding the protection of their patents (Kraker - lever, Wahl Equipose - balance shape, Pilot yellow dot on the fist Capless version ...). In some of the cases they did not have to sue, but the other manufacturer got the message ...
The possible answers as why Sheaffer did not sue this company might point in a direction that will help narrow the search.
Responses
www.newpentrace.net