CSRS limitations
Primary source
Verbatim text below is from the Electronic Code of Federal Regulations (eCFR), a public-domain U.S. government work. Always verify the current version with the eCFR before relying on it for any legal matter.
Full Text
(a) A court order awarding a former spouse survivor annuity under CSRS is not a court order acceptable for processing unless the marriage terminated on or after May 7, 1985.
(b) In the case of a retiree who retired under CSRS before May 7, 1985, a court order awarding a former spouse survivor annuity under CSRS is not a court order acceptable for processing unless the retiree was receiving a reduced annuity to provide a survivor annuity to benefit that spouse on May 7, 1985.
This is legal information, not legal advice. Laws vary by jurisdiction and change frequently. Always verify current law with official sources and consult a licensed attorney in your jurisdiction for advice on your specific situation.