In J. Ray McDermott Co. v. NLRB, 571 F.2d 850, 858 (5th Cir.), cert. denied, 439 U.S. 893, 99 S.Ct. 250, 58 L.Ed.2d 238 (1978), for example, the court held that the passage of more than six months from one refusal to bargain does not bar action by the Board on a timely complaint based on subsequent refusal.