We have the old plate deal in Georgia as well, we are supposed to keep our real plate and current sticker on it in the car. My 69 black plate has never been challenged yet, and yes I keep the real one under the seat at all times.
As do I. Didn't stop Barney Fife from writing me for using 43 year old license plates. Asked him to run the plate, he told me he didn't need to since he could clearly see they were expired.