Radio Station Only 78 RPM'S

These 78's I got in the free bunch are all marked not for sale, they were for radio station use only. I have one more marked like this and one cover has Zeeland radio on it so I think that's the place this person worked. I think this because other records have this system of numbers on them.
I think it's nice to have early social media history like this and although I have newer albums I will enjoy my new collection. I'm sure we all have friends who say they never run across this type of thing, but when you ask them, they don't really get out and put in the time to look. Hope you enjoy.