"The quote is known world-wide" - sorry but that's nonsense.  You talk like it's one of history's most significant utterances and that's plainly not true.  The existence of the guideline is exactly to prevent this kind of absurd "I think it's famous" "I think it isn't" unresolvable nonsense.  As for the context in which this quote is being used, it's in the introduction of an article in which its purpose is to illustrate that the opera was harshly described by some critics.  The fame or otherwise of the quote couldn't be less relevant.  "musicologist Joseph Kerman called it" contains all the necessary information.  200.83.101.199