The Ringmaster kit #S1-A that I checked today didn't have any specific dating on any of the plans or paperwork. The kit box was yellow, which I think was the first iteration, and it had a zip code on the end panel. Zip codes came out in 1963 which is well past the OTS cut off, but I think the S-1A came out later than that. My foggy memory suggests it came out about the same time as the Hellcat. I have to compare the plan but I think they share the same wing. It may have been that Sterling introduced the more modern S-1A to be able to retire the original Ringmaster, and share some parts with the Hellcat to help cut some costs, always of interest to kit manufacturers. Maybe a google search of Sterling kit collectors web sites may turn something up. I remember seeing one years ago.
Type at you later,
Dan McEntee