I am not using the phrase ‘fake news’ in the way Trump uses it (to seed doubt and cast aspersions). I mean to say: “sometimes, I know the details (inside story) of a story/situation. When I read an article about it - I can always tell precisely what got misreported or misinterpreted - which causes me to wonder, what else is getting (mis-)reported like that - about things I don’t know”. Probably the choice of the phrase ‘fake news’ is too extreme. I meant to convey a more subtle point.
That is using 'fake news' the way Trump uses it - 'news reporting I don't like or I think is in some way wrong' rather than 'news that is actually fake with the deliberate intent to mislead'. What you seem to be talking about is sometimes called 'Gell-Mann amnesia effect' - a term I also think is pretty awful (for different reasons) but again, that's not 'fake news'.
Leaving that aside and to your actual point - one way to think about this is 'what major journalistic mishap could have been fixed/avoided by crowd annotation'. Judith Miller's reporting in the run up to the Iraq war? Wen Ho Lee's case? Jayson Blair? It doesn't seem obvious to me it would have made a whit of a difference in any of those nor many others.
