A12 - I suppose that's possible. The cars I had with tips had no evidence of post-factory modification, though.
I'm thinking either the cars were re-directed, or dealer-traded, or the regulations were effective Jan 1st (as opposed to model year), as so other regs many were.
Most of my cars were bought from older "regular" folks, not performance-minded people.
No way to prove the air cleaners one way or the other, though everything seemed the same age - I've always avoided pieced-together cars.