The TVTropes Trope Finder is where you can come to ask questions like "Do we have this one?" and "What's the trope about...?" Trying to rediscover a long lost show or other medium but need a little help? Head to Media Finder and try your luck there. Want to propose a new trope? You should be over at You Know, That Thing Where.
Closest thing I can think of is the Weird Al Effect.
I didn't write any of that.
Also Older Than They Think. The second bullet point on Fan Myopia also mentions something similar ("Failing to realize that a joke in their favorite comedy is actually a reference to something that was already famous").
Seconding Older Than They Think and Fan Myopia, and adding Pop-Cultural Osmosis for references where people know something's a reference, but may not know what it's a reference to.
^ That... is not really related to this, except in the most tangential sense. (say a character who originated as a side character in a largely forgotten work)
When a Shout-Out becomes so popular that people start referencing it directly and forgetting that it was already a reference itself. "Kick ass and Chew Bubblegum" is more likely referencing Duke Nukem 3D than They Live!, "I reject your reality and substitute my own" is more likely referencing Mythbusters than The Dungeonmaster, 11 being a "ridiculous and not even funny" number is more likely referencing Kingdom of Loathing than Negativland, that sort of thing.
I think we just don't have this one, but I wanted to make sure.