I'm glad you mentioned the donkey puzzle, Barnacle. I think it's my favourite puzzle since I started doing Listeners a couple of years ago. It also illustrates my point perfectly: Eeyore's name is common knowledge, Modestine's is not, although if you type it into a search engine, the source comes up immediately. If I remember correctly, I think it was possible to complete the endgame without being familiar with the trick, although, as you say, it was interesting to discover and certainly helped.
In my original post I was merely trying to help Jack Aubrey by pointing out that, unless you are over 60, the title and text of this week's work is not particularly well-known, although the producers and another aspect of the work are familiar. I'm slightly puzzled as to why I was picked up on the word 'niche'. Perhaps I should have said 'not widely known'.
Of course, your general knowledge depends on what you have come across in life, and some people acquire more than others, but there is also common knowledge which is facts, names etc that are familiar to many people and is often the material for general knowledge quizzzes. For example Paris is the capital of France is common knowledge, Ouagadougou is the capital of Burkina Faso is not - at least for most English speakers. Many Listener puzzles draw on common knowledge.