If the standard length was 14 or 16 inches it may well have been an adapted tool-chest-fit for the original owner.
I must confess that my interest in old saws is always enhanced when I see the name "I Sorby".
I bought an absolute beauty about 30-odd years ago from 'Penny-Farthing' in Salisbury. 10 inch plate, I have adapted it to 12 TPI, never any slop in the handle at all and I still use it regularly. More importantly, the pistol-grip handle is such a perfect fit, hand wise, that I used its profile to make a template for subsequent restorations. It has I Sorby 'Northern Tool Works' on the spine.
It must be the thick end of 150 years old.....unusually for a saw of this age there are no marks or pits on the plate. Nor is there a 'Mr Punch' anywhere on the saw.
Sadly, proper tool shops are extinct now but that place was a handy half-way stop to Blandford and you could park in the street outside in those days.