"SJ" ("Small Jumbo" - OXYMORON ALERT!) normally means 16" or so across the lower bout. "000" means about 15" or a fraction more. I assume using the two designators with a slash implies the width is somewhere in the middle, which would make it close to the same width as a standard (Martin) dreadnought. But if so, it would give the impression of being slightly smaller because of the narrower waist. It would be somewhat easier to hold and play, seated, for the same reason. I guess.

Peter