The question is, when was the divorce executed? That’s the language used in the IRS regulations.
https://www.irs.gov/forms-pubs/clarification-changes-to-deduction-for-certain-alimony-payments-effec...
Two different legal websites indicate that the execution date is the date when the document is fully signed and notarized (if notary is required). I am not an attorney, and if I were you, I would not rely on the advice of the Internet. I suggest you ask your family law attorney when your divorce was executed.
(I am also quite puzzled as to why the divorce would not to be final until nine months after it was executed. My ex-wife and I were separated for two years, but when we decided it really was over, the divorce was executed and effective as fast as we could get the judge to sign the papers.)
In any case, if you claim an alimony deduction and provide your spouse‘s Social Security number, and your ex-spouse does not claim corresponding income, the IRS will investigate both of you and make a final determination based on the documents and proof that you can show them.
