Hi Cathy,
Around 1910, Davis started with the common 15x1 on some of their machines. The New Minnesota A started with the Davis Long and switched over around this time. Whether Sears was responsible for this switch or it was a matter of using a more common needle or both is open to speculation. Eventually all Davis machines except the leaf tension on top of arm models (M & N) went with the 15x1. The NVF or "New Vertical Feed" was first made around 1912 and always used the 15x1 or "Davis Short" throughout it's production.
Jon