The Patent date only shows you how early it could be, as you found out.
Like all those puzzle boxes that people say are 1889, that's the oldest they can be, but are likely newer.
In fact, likely are newer. From patent date to production date would likely have taken some time, especially back then.
Here's my understanding:
The VS2 which preceded the 27 is the same size as a 27, both are full size machines. The 28 (VS3) is the small one.
If you can give me some measurements, I can compare to my 27 and VS2 here. The tensioner on the left (face plate) and the single (left) slide plate on a 15 series is what tells me this is not a 15 series. The VS series have always had the 2 long front and back slides plates and the shovel shaped plate at the top and a long bobbin in a "bullet" or boat shuttle, as far as I know.
But I'd be happy to have any updates or correction to this...