SELECT C.customer_name, C.subscription_date, COUNT(*) AS orders_count
  FROM Customers AS C
       INNER JOIN
       (SELECT O.customer_id, DATEADD(MONTH, DATEDIFF(MONTH, 0, O.order_date), 0) AS date
          FROM Orders AS O
         GROUP BY O.customer_id, DATEADD(MONTH, DATEDIFF(MONTH, 0, O.order_date), 0)) AS O
       ON O.customer_id = C.customer_id
          AND O.date >= DATEADD(MONTH, DATEDIFF(MONTH, 0, C.subscription_date), 0)
          AND O.date <= GETDATE()
 WHERE C.subscription_date <= GETDATE()
 GROUP BY C.customer_name, C.subscription_date
HAVING COUNT(*) = DATEDIFF(MONTH, C.subscription_date, GETDATE()) + 1;