It is possible for a 70 model year car that was bought and registered before Dec 31, 1969 to have black and yellow plates. There's a yellow 70 340 3spd 'Cuda that comes to spring fling with black and yellow original plates.
I heard they used the black and yellow plates until they ran out of them in early 1970. This particular car was originally sold in Reno Nevada in Dec. 1969. I still have those plates.
