Hello. Unfortunately, this is not my area of expertise within keys, but I'm happy to share what I do have. I took a look through some catalogs and did some quick searching, and I was able to find nothing about the S keys sadly. I did find the P chart that Pete posted, but I also found the R chart (1-72) if that would interest you. Just let me know and I can put up a photo of it. I'll keep doing some searching into the S keys when i get more time. Sorry I'm not currently too much help on the S series. Looking forward to your article when you finish it if you wouldn't mind sending over a copy