Contagem distinta por ano fiscal e exibe todas as datas no resultado da consulta

SELECT
order_date,
SUM(rn = 1) AS quantity
FROM 

  (SELECT 
  order_date, 
  row_number() over(PARTITION BY YEAR(order_date - INTERVAL 2 MONTH), customerID ORDER BY order_date) rn
  FROM customers
  ) t
  
GROUP BY 1;