I used to have a friend with whom I would talk about rock bands. On more than one occasion, he referred to a group as being "derivative" of another group, when

I used to have a friend with whom I would talk about rock bands. On more than one occasion, he referred to a group as being "derivative" of another group, when chronologically, the group he was calling derivative came first. His response was always that the "derivative" group jumped ahead in time to hear the newer band, and came back and played their derivative crap back in their time. Moral of the story: the late '60s through the late '80s were an undocumented golden era of musician time travel.