But I was more surprised that the show is recycling unused subjects in the main game. In the bonus round, sure, no problem, but given that half of the front game is identifying the subject, it seems like a bad idea to give a team the opportunity to think, "Say, wasn't Cocoon one of the available subjects in that episode we watched recently?"
I think it depends on how the season was taped and aired. If the entire season was in the can before any episodes aired then it's a moot point, so long as the competing teams weren't in the audience for its previous mention.
Assuming a 5/day, 5/week schedule, this would be some time in the 2nd week of taping. Also, if the early episodes had aired, both teams would in theory have been exposed to it could game plan accordingly.
Another potential explanation specific to just this topic is that the 2nd Cocoon episode would've aired close to when the Cocoon sequel would have hit theatres. Maybe someone thought pushing out a topic related to then-current events could increase the show's popularity.