There is no problem.In your certificate verification, duplicate will be treated as orginal only.Generally the duplicate copies issued by the board or college will have signature of the authorities below it. Please check it and if it is a unsigned document then go to the school or college with the copy of your application for duplicate copies and get it attested and get it signed by the concerned principal of the college. You must get the seal of the college also below the signatures.A signed duplicate copy is as good as the original one and you should not have any problem at the time of document verification.