Yeah, this is a great question. I can argue both sides as well. Unfortunately I'm a TPA, not a lawyer, so no one expects to pay me to do so.
My own opinion is if it is an irrevocable, legally binding order, it should count a/o the date of the order, much like mailing a valid check by 12/31 counts as a payment. But the reality is recordkeepers' systems are programmed in a certain way, and the 1099-R will be driven by the system. And it's pretty much impossible to get them to override this process or revise a 1099-R.