Update: bought a pack of ten for $5 at AZ and installed, bingo! It was two bad bulbs... What are the odds?
Evidently pretty good. I had two bad bulbs in my Lightning, that I had ignored for quite some time. When the truck was in the shop after being t-boned by another driver, they replaced them. Both bulbs in my Ranger have been burned out for years. But at one time, one of them did work. I just ignored it, and finally the other one burned out. I'm ocd, my truck is clean all the time. Even clean the rear suspension since it's visible to anyone following. But not about license plate lights, don't care if they work or not.
Who knows, maybe one of them on yours has been burned out for some time, and ya just didn't know it.