Oh sorry, heheh, your message came right after I posted mine so I thot you were talking to me. Stan has all the Singer models up thru the R4 but none after that. He did not like the painted R5 and the Later S versions were too modern for him.
And yes, Loewy did design the S series. I have a feeling he, or some other noted designer, Dreyfuss perhaps, also did the R series -- they are just too beautiful not to have conceptualized by a high-end industrial designer. In-house artists just don't come up with stuff like that!