It's documented that Tim Child, creator of Knighmare, used to plan the quests out for that from start to finish across the three levels of the game and behind every door, and of course it had been a complete waste of time planning levels two and three if somebody "died" after three rooms. It was later changed to planning on a per-level basis.
It seemed to work on how many mistakes the teams made along the way as to how lenient the producers were at allowing them to continue or not! I seem to remember some very questionable survivals including one in the corridor of blades!
Had more to do with logistics, if somebody falls off a spinner in the first couple of rooms (as happened in one episode) and the next team hasn't arrived in Norwich yet, its probably easier in the long run to give them the benefit of the doubt. Mind you it worked both ways - the way the final (as it turned out) series ended was controversial. The last but one team skipped an entire level (by design) and ultimately won the game.
I always thought it a bit of a con how the contestants had to be ‘rescued’ at the end of a series no matter if they were in Level 1 or Level 3, shame they couldn’t have edited the show slightly more tighter so all quests could get played to completion (or death!)
I'm not really sure what is worse, having a quest terminated by the end of the series or having a quest ending naturally and a gap of heaven only knows how long to fill at the end of the final episode of the series. I suppose they didn't know how long the teams were going to be playing for, in the early part of a 16 episode run its relatively arbitrary and I wouldn't be surprised if it was edited as they went along.