What category covers true 'unknown unknowns' that models cannot account for because they have no historical precedent in the training data?

Answer

External shocks

External shocks are unforeseen events, such as a global pandemic or a sudden regulatory change, which have no historical parallel and cause even sophisticated models to revert to guesswork until new, relevant data is collected.

What category covers true 'unknown unknowns' that models cannot account for because they have no historical precedent in the training data?
modellimitpredictiondatastatistic