Hi, and welcome to the forum.
The s2 and the s2 super were in the S/N range 223001-636891. Production might have overlapped since the Super was only sold in Japan. But in your case I would assume that your camera has been in for a repair and that the top plate was changed. Spare tops have serial numbers outside of the ordinary production run.
Collecting Pentax is fun, and the S2 by itself is fun due to many versions like Asahi Pentax S2 or H2, Asahiflex S2, Penta Asahiflex S2, Honeywell Heiland Pentax H2 and Honeywell Heiland Pentax H2 Store Demonstrator, then the ones marked Asahi Pentax SB, and the S2 model II called super sold in Japan as well as the SB2. Add to that chrome and black verdions. I've even come across a model engraved for sale via US bases. SB and SB2 were for sale to Japanese defence forces. A fellow collector found one of those in Manila.
Best of luck collecting all of these beauties.
Dont forget to use them.
---------- Post added 03-25-2017 at 12:54 PM ----------
I forgot to add that the S2 came with two types of speed dials, without or with notch for clip-on exposure meter.
The S2 super came with two different types of film counter, old version with manual reset and new version with automatic reset of the film counter.
Last edited by Baard-Einar; 09-13-2017 at 02:32 PM.
Reason: Spelling errors