The best thing would be to contact the company for instruction on what to do with the extra "D" certificate. It will most likely get voided out during the registration phase so, best to find out which one will be valid and which one will not.
You should turn in the 2nd certificate and get it converted. Is it too late now? The reason you received two certificate's is because you invested an amount of money that warrants two certificate's. Most people received one because they did not invest as much as you!
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