seq for Date class arguments.refvalIdxByDate(t0, b, w, epochStr, epochs)"1 month", "1 week" or "1 day"t0 go i, i= 1,...,b years back in time.
  For each year, go w epochs back and include from here to
  w epochs after t0.
  In case of weeks we always go back to the closest monday of this
  date. In case of months we also go back in time to closest 1st of
  month.