Just measured my 4/4 outside of front wings and it’s 1,400mm.
However in the brochure it says 1,630mm (must include mirrors) Plus 4 says 1,720mm
Hope this helps
I think youre right that on our everyday cars the door mirrors are a fixed position and thats where manufacturers take the overall width measurement. But on Morgans the mirrors can be angled so the overall width changes. Also on the 4/4 the outside width difference of the front and rear wings is different than a Plus 4, the rear being the widest point on a 4/4.
Maybe the factory measurement could include the possibility of full width bumpers being fitted, who knows!