Jeff Gunn

How do over strikes occur in the minting process? are the individual over struck numbers letters/numbers individually applied by hand in some form of QA check/process after the initial striking of the coin? if so should the really be considered a variety? the reason I ask is, theoretical if it hand struck then you could possibly have endless possibilities/combinations sub varieties to consider. Not that I am distracting for the these anomalies but when collecting a date run for instance should they really be considered a variety or an anomaly?