From the article, > Paolo Galli, who found the note in the Apostolic Vatican Library while looking for contemporaneous accounts of another historic Italian ear

From the article, > Paolo Galli, who found the note in the Apostolic Vatican Library while looking for contemporaneous accounts of another historic Italian earthquake... Sounds like he was being thorough in his research. It's not like we have millions of books from back then, it's plausible he read through every book in a date-range. But also, this pre-dates our understanding of the mechanics behind earthquakes: god was to blame. In some sense, where better to look, than a book of appeals to god?