Re: episodes that are part of two different TV series
The Star Trek DS9 episode 'Trials and Tribble-ations' was released on DS9 Season 5 Disc 2 and on TOS-R Season 2 Disc 5.
While it's cute that "Trials and Tribble-ations" got a release on the TOS-R DVD set, it's really not a TOS episode in any sense of the term. It's a DS9 episode that happens to feature TOS characters and a TOS setting.
"Every line of serious work that I have written since 1936 has been written, directly or indirectly, against totalitarianism and for democratic Socialism, as I understand it." - George Orwell, 1946