I think I might have solved the "cut-pile" or "80/20 loop" carpet mystery

For what it's worth, my parents' 62 Dodge Polara 500 convertible had very thick, dense cut-pile carpet. My old 73 Duster 340 (which I haven't seen in 40 years) had, as I recall, much thinner, less plush cut-pile carpet. My 67 Charger and all three of my A body Barracudas (65, 67 and 69) originally had (and still have) loop carpet.