In watching the clip again, I'm wondering if, in any of the interviews they'll mention that Jan Chappell almost didn't appear in the location shoot for the episode "Redemption" because she didn't approve of filming at an active nuclear power station and was quite vocal about it, so she would have been separated from the cast at the beginning and would not have appeared again until the end.
She had it written into her contract after this episode that she would not do any location filming at any nuclear power plants, which is why she stays behind and mans the teleport in subsequent episodes shot in or around nuclear power plant.
Then there's the story about how the cast and crew didn't eat in the nuclear power plant's cafeteria because there were signs posted reading "Danger - Possible Contamination", so they would all go to the local pub to eat.
Wasn't Chappel pregnant at the the time adding to her concerns.
As for the interviews being arhival from the early 90s, guess it must been a cost/rights things because as I've mentioned between there was a lot more update interviews on youtube from proffesionally produce retrospective that covered the first 3 series but didn't have the funding available to do the fourth.
Then again also on youtube can find videos of conventions from the 90s where Darrow and Thomas come out with cigarettes in one hand a drink the the other that wouldn't happen in this day and age
