Interesting info via Needlebar about my 115...I asked about the serial number and it being listed as a Dec. 20, 1911 commission model 27, because, quite frankly, it bothered me!
I got this information from Chrys, who is a super whiz regarding all things "sewing machine"!!
"As Carol pointed out the Singer charts have some errors. The charts also have some changes from the first time they posted them. The models that say St. Jean were shipped there for final assembly. The heads were cast at Elizabethport. They did that because St. Jean was behind on production.
So it looks like your 115 on December 1911 is the earliest serial number I have come across. You have to keep in mind that when a company like Singer introduces a new model, they could have easily spent a year developing it. So it is likely that small batches can turn up before the actual start of large production numbers."
I had just assumed that there was some kind of serial number error and that my 115 was made with the first run of 115-1 machines that have a date of March 1912... someday I'll learn not to assume when it comes to sewing machines!! Still *SO* much to learn!!