The S .. I have heard comes from the Swiss market or for Swiss production...not sure though.
The body is heavier, bulkier, and it feels a little cheaper in terms of materials, a little like the Delicias ..
I found the volume muted.. and keyboard narrow.. and action lighter, less stiff than the IIIR . It might have a different reed setup.. or tuning ( for Swiss playing )..but that too needs ascertaining. I had one in BbEbAb... which is big in Switzerland/Austria for playing with brass bands.. or with the Colombian vallenato players..
Overall the IIIRS looks better that it sounds in my opinion.. but if internally mic'ed and with Zydeco Joe at the wheel .. I am sure it passes with flying colors..