Check and see if your originally scheduled flight left on time. When I called for original routing credit (ORC) they checked if those flights were on time and gave me credit if they were delayed. Note, this happened even when I was rescheduled before the delay.

For example I was flying DFW-STL-ORD and caught a nonstop about five hours earlier. Of course I got less miles this way so called a week later to ask about getting ORC. I was told "because you volunteered to take the direct, you lose out on the miles from taking two shorter trips".

One month later, I did the exact same thing. I figured why not give it another shot and called again. I asked for ORC and the agent said, please hold on they have to check something. She then came back and said "I'm sorry, I do see that your flight to St. Louis was delayed by over an hour and I will be happy to post the miles to your account" Note: when I left on the non stop, this was hours before my scheduled departure and at that time, the flight was on schedule.

Of course YMMV, but here is one more data point.