Because the quatrains supply no date, no reliable place name and only oblique description, applying them to a real event is almost always retrospective: a reader with the outcome already in hand searches for a verse that can be bent to fit it, and quietly sets aside the many that cannot. The clearest demonstration of how easily this generates convincing-looking hits is not a genuine quatrain at all. In 1997 a Brock University student named Neil Marshall wrote a deliberately vague four-line passage for a class essay, meant to illustrate exactly this mechanism, and did not attribute it to Nostradamus. After the September 11 attacks in 2001 the passage began circulating online as a genuine, centuries-old prediction, with further lines added by later, anonymous hands, one of which names a date decades after Nostradamus's death. Fact-checking organisations traced the text back to Marshall's essay within weeks, and no version of it appears in any sixteenth century printing of Les Propheties.
The episode does not by itself settle whether any authentic quatrain has ever been fulfilled; readers who consider that question open point to matches, such as the Hister verses, that use genuine sixteenth century text. What the 9/11 case shows is how the mechanism works once a match is wanted: obscurity supplies the raw material, hindsight supplies the fit, and at least once, an invented text supplied the rest.
Sources Did Nostradamus Predict the 9/11 Attacks?Snopes.com editorial staff with The Unknown NostradamusPeter Lemesurier