Hektor,
There are three main variants of the Vito B: the earlier body type which are shorter, with no bright frame in the viewfinder has two variants, the early version with a non-rectililear focussing helicoid where the whole lens rotates, and a later one with a rectilinear helicoid. Then the later body with a taller superstructure with a larger viewfinder incorporating a bright frame.
Apart from this most obvious difference there are lots of less obvious ones, such maximum and minimum aperture of the lens, shutter type (and variations), minimum focussing distance, etc. There are also minor variations such as tripod bush construction and marking differences too.
Good luck!