5 C.F.R. § 839.1002

Will OPM compute the lost earnings if my qualifying retirement coverage error was previously corrected and I made TSP make-up contributions?

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If you made contributions to the TSP after your qualifying retirement coverage error was previously corrected, OPM will compute the lost earnings on your make-up contributions to the TSP under the following circumstances:

You were in:And were
previously corrected to:
And under these rules you elect:
CSRSFERSFERS.
CSRS OffsetFERS
Social Security-OnlyFERSNo election required.
Social Security-OnlyCSRS
Social Security-OnlyCSRS Offset