Good question. My guess:
The cab does not include the doors (windows) - 47-53
Cab windows are installed in the “cab-body”.
3 windows are standard, and 5 windows are optional.
Of course, that explanation does not work in 54/55st - they would have 2-window or 4-window cabs?
If you count all windows, they would be: 5 window, 6 window, 7 window, 8 window, or 9 window? (47-55st)
Is that confusing/logical enough?
