To clarify (now that I have more info)... Dad retired in 1981, and elected retirement allotment and survivor benefits for his wife. They were divorced in 1985. Both parties had intended for the SB be in the divorce judgement, but somehow it was missed.
Dad was overseas some 20 years post divorce. All the while, he continued to pay on the SB election he had made for his former wife. It was not until the end of last year, when he wanted to increase her allotment, that he was informed that she was no longer a beneficiary of his survivor benefits. He has continued to pay because he hopes for this modification to correct the issue.