Wow. This is some great find that was made on these U.S. 1/2 cent postage dues (J88) used on cover. It is interesting that their location of Ottawa, OH has helped to find many more of them. How many years have collectors been looking to find them on cover? This forum is a great place to announce such finds. Even though I don't collects these stamps and covers, I always enjoy it when stamp collectors find such items and post them on here.
It's fun to find something new and I've done several it times over the past few years. I'd been looking for J88 on cover since I was a teenager - so 50 years.