I may be a little late on this reply, but I just picked up a 20 gauge Sportsman version of the Remington model 11 and may have some info to help. I too had questions about the serial number. 1st off, my serial didn't fall into the ranges kept on file at Remington. My Sportsman 11 fell in line with the serials on the regular Model 11 in 12 gauge, not the Sportsman in 20. Secondly, the date code on my barrel translated to December of 1948. As far as the Remington website is concerned, the Sportsman and Model 11 were discontinued at the end of 47 and replaced with the 11-48 and Sportsman 48. Also, my Sportsman did not have an S in front of the serial.
So I called Remington and spoke with a very knowledgeable lady in their historical records department. She informed me that the 'S' in the serial number was not always stamped in the same place on the receiver, although it was usually in front of the serial. As it turns out the S was kind of an afterthought and was lightly stamped into the receiver after they had already been serialized. Also, because the S was so lightly done, if the gun had been polished and reblued the S may not even be there any more.
As far as my date and serial number discrepancies, my Sportsman was probably one of the last to leave the factory due to the late serial number and date code on the barrel. She went on to say that during and for a few years after WWII some records were not kept well or were outright lost, so the documentation we have today is in some cases a best guess.
She told me basically that if it says Sportsman on the bolt (Instead of Model 11) and only holds 2 in the tube without an actual plug its a true Sportsman, despite what serial number records have to say about it. She also mentioned that the date codes on the barrel often do more 'harm' than good in identifying the gun. I'm not exactly sure what she meant by that but I would assume they're a decent guide but not exact.
My particular Sportsman is marked Skeet on barrel and is 26" long. I was itching to use it, so I took it to a trap range that is on my way home from work. The shotgun functioned perfectly and I shot a 20. Not too bad for a 60 year old skeet gun! Take it out and shoot it, clean it and love it! Just make sure your recoil rings and spring are set up for the loads your using and it'll probably last another 60 years.
Just my 2 cents.. Hope it helps someone someday...