Must I file a request for a refund within a certain period of time?
Yes. Any request for refund must be filed within two years from the date the fee was paid, except as noted below.
Any request for refund based upon a deposit account charge must be filed within two years from the date of the deposit account statement indicating such charge, and include a copy of that deposit account statement.
Refunds based on later establishment of small entity status must be filed within three months of the date of the timely payment of the full fee. (See 37 CFR 1.26 and 1.28.)