I think this issue is like the chicken and the egg...
Where do we place the 1918 Dodge convertible coupe (actual name) that was
what I consider to be the first 2 door hardtop convertible. Removeable "B"
pillar and windows that either wind down or slide down (rears). Leaving what
is more commonly called a convertible hardtop coupe.
For the necessary Imperial content -- The first Imperial 2-dr hardtop is 1951.
Sherwood Kahlenberg