我某化工进出口公司向乔治亚有限公司出口一批化工原料。我出口公司根据合同规定的5月份装运期，提前于4月5日即向乔治亚公司催促开证，但对方一直延迟到5月5日才开出信用证。信用证中有关条款如下：“…negotiation onor before June 15，1997． …2/3 original clean on board ocean bills of lading madeout to order of Georgia Co．Ltd．，notify accountee．The bill of lading must bedated not later than May 31，1997． All documents must be negotiated within15 days from the date of bill of lading．”信用证中的特别条款同时规定：“Thebeneficiary must send 1/3 original bill of lading to the accountee immediately after shipment．...A facsimile certificate issued by the applicant certifying that the consignee has taken delivery of the goods at the destination．”我化工公司在5月13日装船，但由于买方在5月30日才发出“收货证明”，造成最后交单日期超过了信用证规定的时间，从而构成过期提单。问：我应该从上述案例中受到什么启示?