Different Front & Back Plates

Here are the plates found on the 37 Cord. Now I'm not sure where the 1947 Plate came from because I do remember removing the 51 plates from the car.

My 1937 Beverly Sedan came with different front and back license plates. The front is a California black plate with the date on it of 1951. Now the rear California black plate is a 1949. Was this because California changed the look of the plates around these years? I have always wondered about this oddity. Pics to follow later.