If you have lost your NIE certificate and you have been requested it recently. You will have to apply for a NIE certificate to be issued again, the process is the same as applying for the first time, although it takes less time to be issued if the petitioner already has a NIE Number as they will run a search on their Records. If after running a search by your name there are no results, you will be given another NIE number. Perhaps you remember your NIE number or you may have saved a copy and it was just the original