Searching for a rare word for "something taken as truth due to having been repeated so much"

Solution 1:

Proof by (repeated) assertion?

… is an informal fallacy in which a proposition is repeatedly restated regardless of contradiction. Sometimes, this may be repeated until challenges dry up, at which point it is asserted as fact due to its not being contradicted (argumentum ad nauseam). In other cases, its repetition may be cited as evidence of its truth, in a variant of the appeal to authority or appeal to belief fallacies.

factoid ?

an item of unreliable information that is reported and repeated so often that it becomes accepted as fact: he addresses the facts and factoids which have buttressed the film’s legend

Note (from same source): North American a brief or trivial item of news or information: how does the brain retain factoids that you remember from a history test at school?

The North American usage is different from the basic meaning of the word.

Solution 2:

How about, "received wisdom"? "The received wisdom is that Alberto Fujimori is responsible for the capture of the head of the guerilla group Sendero Luminoso, but in fact he had nothing to do with it." Also, "accepted version"?

Solution 3:

Woozle Effect

Or just woozle, referencing the woozle in Winnie the Pooh for which the only evidence is the reports of the woozle.

Proof by Citation

Solution 4:

'Apocryphal' is the word I've heard for this. The dictionary says it means, "of doubtful authenticity." But colloquially I think it often implies doubtful but often thought to be true (because it's been repeated).