Yep - the 70s copies pre-date the trademark registration, so (provided they don't have a Ric logo) they don't infringe it.
And anyway, they are no longer available new, so it's just chasing shadows on the 2nd hand market.
However, I do have respect for the way they have stuck to their original base and not sold out & offshored.
And those current Chickenbackers are awful!