Several years ago my wife got a ticket for her car not being registered. It was registered but she didn't put the stickers on the plate. She had renewed the registration but didn't know about the stickers for some reason. The stickers were still attached to the registration in the glove box.
I thought for sure they would waive the fine once I proved it was in fact registered but when I spoke to whoever it was that you raised those sort of objections to they informed me that the car wasn't registered until the sticker was on the car. They could waive the fine if the sticker had been stolen but not if you didn't put it on.
About a year earlier we got a ticket because our car hadn't moved in three days. It was parked on the road and I don't think it it been marked or anything but it had snowed and three days later our car still was covered with snow. I'm guessing they just ticketed anyone whose car had obviously not been driven. Both of these things happened in Provo.