I have posted on this previously. My father bought C3109577 new. I still have the tractor.
The serial number bothered me for a long time. I wrote to Case in the 1970s and was told it was a 1927 model. I thought wow I have a rare prototype, but it has many late model features. I knew that my father had not changed the tractor much, but one of his brothers was a good mechanic and had worked on it at times.
I then wrote to Dave Erb. He told me that in 1936 and 1937, Case made so many tractors that they had to use a 7 digit serial number, but to get the year you use the 6 digit formula.
Over the years I have run across several C tractors in Australia that fit this pattern.