But the OP's "intent" with this thread is thin. A TV series' episode appearing on another series' box set doesn't make that episode "part of that series."
Geez, why are people getting so hung up over the topic title? Just pretend the topic is "episodes that are part of two different TV series' box sets" and all will be right with the world.
Probably because there not that many examples of this!!! But is also done as just a marketing stunt without any connection between two series. I know Warner Bros did that a few years back.
Your real topic is limited!