I'm definitely struggling to think of any non-proper tunes which accidentally became proper tunes. I'm not convinced it works both ways.
like I said I don't wanna dig rn, I gotta go to sleep
but I am convinced they exist, if only as rule-proving exceptions
it does depend where you draw the boundary on proper tunes
for example "Marquee Moon"
I guess they weren't TRYING to make it unapproachable, that's just played guitars and wrote songs in a real fucking unusual way
but I heard that in a Starbucks the other day
"Autobahn" + that kinda thing, as mentioned w/Kraftwerk