I have a vintage Oregon "Pacific Wonderland" plate on my '57 Chevy with a current "Special Interest" sticker. For use in car club related activities only, such as parades or car shows. Put 4,400 miles on it the summer of 2018 on a road trip to Minnesota & back. Went to a car show in Henderson, MN during the trip. So while it may be a bit of gray area, in the letter of the law it was completely legal with the intended usage.
Last week I got a Special Interest plate for my '91 Caprice as it is over 25 years old. DMV quizzed me on the usage. To illustrate how often the car is driven, I showed them my 2019 tags (issued in 2017) which were never installed on the plates. They backed down. I got tired of shelling out money every two years for a car that is rarely driven.
-Eric
