code: def get_zeroth_quarter_idx(self, stacked_last_per_qtr):
          previous_releases_per_date = stacked_last_per_qtr.loc[
              stacked_last_per_qtr[EVENT_DATE_FIELD_NAME] <=
              stacked_last_per_qtr.index.get_level_values(SIMULATION_DATES)
          ].groupby(
              level=[SIMULATION_DATES, SID_FIELD_NAME],
              as_index=False,
          ).nth(-1)
          return previous_releases_per_date.index