From the info I have and from what Bruce told me it was only a 1 year model (1949)
But I think a few may have snuck out in late 48' as a Brochure I have is dated 48' and is introducing the "New" 12B Power Ho
The NPR6 engine on mine is dated 48'
The 12B was a model for 1949 & 1950.
Brian's B&S NPR6 engine was made in May, 1948.
Keep in mind that the model year and the calendar year were not always the same. (New models of cars, trucks, tractors, and other equipment were often debuted prior to their model year.)
Production of the 1949 tractor models would have begun in mid-to-late 1948, and some shipments to dealers may have been made in 1948. ....Literature would have also been printed in advance of the calendar year.
There is also no way of knowing when the production of a certain model tractor stopped. .....If production was stopped in February or March or April (for example), it would still be listed as having been produced in that year, but there is no guarantee that production continued beyond that point.
Also, sometimes Bolens (and other manufacturers) would list a certain model as a current model, although production had been discontinued previously, but the factory had a lot of "left-over" units to sell.