Sure, copying is possible and happens often. But isn't the more probable explanation for pretty much each one of these examples, that the designs are simple and the designers got to the same place without knowing their niche German graphic design history?
I think so too. There are some solutions which are just so easy for multiple people to stumble across in their explorations without ever having seen the "original".
Take the idea of a chevron in half of an "X". I've seen that idea done dozens of times and even unintentionally stumbled across it in my own studies without having looked/thought at any particular example.
Most everything is copied, but with a slight / major variation.
Designers read blogs,newsletters,forums,etc for inspiration, so when they found some inspiration they also have picture in mind how to do their on work, So when they design they influence by that, finally it's not called copied, i call it inspiration :-)
Be it coincidence or coming up with the same solution, it happens. If you 'call someone out' on it though, it helps if you keep this in mind and actually use your eyes https://mobile.twitter.com/tldnr/status/668732496163549184
Does it count as copying if you do it without being aware of the original?