Singer was known to stop production of a model to produce one or two machines of a different model, but they didn't change the registry for the serial numbers...
My 115 is like that...if you look up the serial number, it reports back to a model 27 made in 1911, but the mass 115 production didn't actually start until 1912. One of the experts on Needlebar tells me that they don't know of an earlier serial number on a 115, and they've been "collecting" serial numbers for 30 years. They also told me that the numbers before and after mine ARE model 27s...