I wouldn't have certified this question to the Arizona Supreme Court.
It's a fact-bound issue in a diversity case: Whether, in this particular context, the relevant state statute of limitations commenced in the 1980s or instead when the plaintiff turned 65 in 2009. That's important to the parties, but not to many other people.
Perhaps the Arizona authorities aren't totally clear as to the correct answer to the question. But that's life. Lots of appeals are like that. The Ninth Circuit is just as good as the Arizona Supreme Court -- or at least nearly as good -- at giving it its best shot.
This is the kind of fact-bound case that, if I were on the Arizona Supreme Court, I'd almost certainly say doesn't deserve review. Regardless of how it came out below. Both sides have plausible arguments, the resolution of the issue doesn't affect many people besides the parties, and we're not talking about grand principles. Let the Court of Appeals decide that one. The state supreme court (hopefully) has better things to do. Similarly, even if the Ninth Circuit gets it wrong, this is not a case where forum-shopping is a critical problem (or concern). You don't have dozens of these types of cases coming up every year.
I can imagine strategic reasons why you might want to certify the question. But from the standpoint of judicial efficiency, this is case that should be put to bed. It's already been briefed in the Ninth Circuit. Just decide the thing. Don't boot it to the Arizona Supreme Court.
Especially when the issue is what disability benefits the plaintiff should receive. He's 68 already, and not getting any younger. Just decide the appeal and finish it. One way or the other.
I like comity as much as the next person. But I'm fairly confident that the Arizona Supreme Court has better things to do than resolve this appeal.