def METHOD_NAME(self, dts: Set[date]) -> None:
    # Observed days are added to make up for any days falling on a weekend.
    if not self.observed:
        return None
    observed_rule = THU_FRI_TO_NEXT_WORKDAY if self._year <= 2012 else FRI_SAT_TO_NEXT_WORKDAY
    for dt in dts:
        for i in range(4):
            self._add_observed(dt + td(days=-i), name=self[dt], rule=observed_rule)