Trademark registrations must be maintained within the first 5-6 years after registration, within the 9-10th year after registration, and between every 9-10th year thereafter.
Unless there is acceptable non-use, Maintenance requires (i) confirmation of use for all goods/services identified and (ii) filing of at least one specimen for each class of goods/services.
Although one specimen is required per class for trademark maintenance, more may be required by the USPTO Post Registration Audit Program. The program "promotes the accuracy and integrity of the trademark register." If all goods/services cannot be supported there are possible penalties to face from a trademark audit.