29 CFR 4041.29: Post-distribution certification.

(a) Filing requirement. The plan administrator must either—

(1) Within 30 days after the last distribution date for any affected party, file with PBGC a post-distribution certification (PBGC Form 501), completed in accordance with the instructions thereto; or

(2)(i) Within 30 days after the last distribution date for any affected party, certify to PBGC, in the manner prescribed in the instructions to PBGC Form 501, that the plan assets have been distributed as required, and

(ii) Within 60 days after the last distribution date for any affected party, file a post-distribution certification (PBGC Form 501), completed in accordance with the instructions thereto.

(b) Penalty considerations. If a standard termination notice is filed in accordance with § 4041.25(a)(1), PBGC may assess a penalty for a late filing under paragraph (a) of this section only if the required information is filed more than 90 days after the distribution deadline (including extensions) under § 4041.28(a).