To paint or not to paint the underside

I see so many hi end restos painted body color underneath that i think a lot of guys believe that's how they came from the factory. I recently talked to a seller who has restored many Mopars and claimed all that he owned back in the day were all painted body color underneath.I took the high road and told him i didn't know that's how the factory did them, and went on my way.

Maybe all his cars were gray ? Lol