code: def _create_historical_estimates(resource, configuration):
      
      today = timezone.now()
      month_start = core_utils.month_start(today)
      while month_start > resource.created:
          month_start -= relativedelta(months=1)
          models.PriceEstimate.create_historical(resource, configuration, max(month_start, resource.created))
docs: Create consumption details and price estimates for past months.
  
          Usually we need to update historical values on resource import.