And probably stolen. Lots of times car thieves will grab a paper tag and put it on the stolen car they are driving. Sometimes they have a stack of them. It makes IDing the car that much harder.
You are undoubtedly correct. I've seen what were clearly fake printed paper tags on several cars. It's a no-brainer, including for those who haven't bothered to renew their registration.
This is a perfect argument for having a city-wide ALPR system. Even if a fake or stolen tag is placed on a car, it can be flagged and searched for in the system. But lacking that, the criminals have a perfect defense against identification - at least for a few more months.
By the end of this year, Apple will release the newest version of iOS, which will allow third-party manufacturers like Tile to connect into their "Find My" network. Apple is also rumored to be gearing up to release the AirTag, their own Bluetooth locator. By this time next year, you'll be able to hide a low cost Bluetooth device in your car, and track it almost as easily as if your car contained a dedicated GPS tracker. Every iPhone out there will become part of the locator network. It's going to become a lot more difficult for car thieves to hold on to a car for more than a few hours.