61 Pa. Code § 119.13a
If a return is filed by an individual and, after his death, a refund claim is filed by a legal representative, certified copies of the letters testamentary, letters of administration or other similar evidence shall be annexed to the claim to show the authority of the legal representative to file the claim. If an executor, administrator, guardian, trustee, receiver or other fiduciary files a return and thereafter a refund claim is filed by the same fiduciary, documentary evidence to establish the legal authority of the fiduciary does not need to accompany this claim if a statement is made in the claim showing that the return was filed by the fiduciary and that the latter is still acting. In these cases, if a refund is to be paid, letters testamentary, letters of administration or other evidence may be required but should be submitted only upon the receipt of a specific request therefor. If a claim is filed by a fiduciary other than the one by whom the return was filed, the necessary documentary evidence should accompany the claim. A claim may be executed by an agent of the person assessed, but in this case a power of attorney must accompany the claim.
61 Pa. Code § 119.13a
The provisions of this § 119.13a issued under section 354 of the Tax Reform Code of 1971 (72 P. S. § 7354).