Maybe I just got lucky, but I emailed the Ambassador desk 3 weeks ago about a missing stay. I reported it as missing 5 days after check-out (because from years of experience with missing stays, I just know it will not post) and the agent immediately credited the missing points / nights.

Like I said, my experience with Ambassador desk has improved significantly in the past few months. But maybe luck also plays a role here (which agent picks up your ticket).