1941-1948 Ford and Mercury club coupes- two different roofs. why the difference?

[V12Bill]

When I was in High School I had a 1941 business coupe and the roof sloped into the panel above the trunk lid with no crease. A friend had a 1941 club coupe with the full back seat and it had the crease. It seemed that post war club coupes did not have a crease. About a year ago I saw a 1946 club coupe at a show and it had the crease. I don't know any details of that car, it may have been an early model. Mercurys used the Ford bodies from 1941 and up. Only the front sheet metal from the cowl forward was unique to the Mercury.