They probably did, but there’s a difference between some guy gluing a piece of paper into a weird shape, saying “that’s cool” then throwing it away, and some science type doing it and writing a paper about it. In general stuff isn’t considered “discovered” until there’s published data about it.
I’m sure you’re right. When Mobius’s paper came out all across Europe there were guys digging through their trash out back thinking “Dang - I wish I hadn’t thrown that doodad out last month - it could have been the Vinkowyz strip instead of that darned Mobius strip.”