Marcelo, you are correct. For years, Ford made two styles of coupes. In the 30s, they were called 3 window and 5 window. The 3 window coupes doors were the same larger doors of the 2 door sedan. The 5 window coupe doors were the same as the smaller front doors of the 4 door sedan. All of the coupes in the 40s (also 39s ) had 5 windows, but the business coupe continued with a big package tray behind the seat and the rear windows were fixed as in the 30s and the small 4 door sedan doors were used. In the opera coupes, the rear windows opened, there were jump seats and the larger 2 door sedan doors were used.
The Business Coupe doors are the "four door type" door. The actual four door, door, has to be modified (ground down a bit) in the upper rear corner to fit the coupe. I have owned at least ten of these old Fords and Mercs (41-48) and I prefer the roofline of the Business coupe. It has less "hump" over the quarter window and smoother lines..