Saw this same question as a poll in the Freewayjim Facebook group earlier this morning. Coincidence?

When I was growing up, Kentucky issued a new license plate every year. They alternated between blue plates with white numbers, and white plates with blue numbers. There was no fancy artwork; just the state name, year, license number, and county name. All renewals were due in December. If you were driving on Jan. 1 with the wrong color scheme, it was obvious that your registration had expired.
At some point, I think in the 1980s, Kentucky went to multi-year plates and changed the registration renewal to the month of the registered owner's birthday. Stickers changed colors every year, and the month number was prominently printed on the sticker.
Now, even that process has changed. Stickers are all gray and the only thing different is that the year is what's displayed in big numbers. If you're not stopped for anything else, you can theoretically drive for months with an expired registration unless you are like me and your birthday is in December. The weather is usually too crappy around here to place the new sticker on the plate.
One year, I had put the sticker on and it didn't adhere very well and started peeling off. I had my registration just in case something happened, and it did one night coming home from work. A state trooper got behind me, saw the previous year's sticker, and pulled me over. I showed him my registration and told him what happened. No ticket, but he did direct me to get a replacement sticker (which cost me some sum of money; it wasn't an outrageous amount but the principle of the thing was irksome.)
Another time, the weather had gotten so crappy that I hadn't had an opportunity to put the new sticker on. I had it in the car. Pulling out of Walmart one day at lunch after we went back to work in the new year, a local cop was behind me and saw the old sticker and pulled me over. I showed him the registration with the sticker ready to go, explained that it's always dark when I get home from work and it had been raining on the weekends so I couldn't properly affix the sticker, and that one time in the past I had done so and it wouldn't stick and ended up falling off. He understood perfectly, so again no ticket.
I'm in general not a fan of windshield stickers, and am very happy Kentucky doesn't have a vehicle inspection program. We did when I was growing up, but that program was abolished and the state instead required insurance stickers when it became mandatory for vehicles to be insured. The stickers were eventually eliminated in favor of cards to keep in the vehicle.