29 C.F.R. § 4050.205 – Filing with PBGC.

(a) What to file. A subpart B plan must file with PBGC the information specified in the missing participants forms and instructions, and if the plan is a transferring plan, payment of—
1. (1) The benefit transfer amount for the missing distributee; and
2. (2) Any fee provided for in the missing participants forms and instructions.
(b) When to file. The plan must file the information and payments referred to in paragraph (a) of this section in accordance with the missing participants forms and instructions.
(c) Place, method and date of filing; time periods.
1. (1) For rules about where to file, see § 4000.4 of this chapter.
2. (2) For rules about permissible methods of filing with PBGC under this subpart, see subpart A of part 4000 of this chapter.
3. (3) For rules about the date that a submission under this subpart was filed with PBGC, see subpart C of part 4000 of this chapter.
4. (4) For rules about any time period for filing under this subpart, see subpart D of part 4000 of this chapter.
(d) Supplemental information. Within 30 days after a written request by PBGC (or such other time as may be specified in the request), the plan administrator of a subpart B plan required to file under paragraph (a) of this section must file with PBGC supplemental information for any proper purpose under the missing participants program.
(e) Reliance. As administrator of the missing participants program, PBGC will rely on determinations made and information reported by plans in connection with the program.