I'm definitely not an expert here, because I've done this exactly once in my life. But when I called to request original routing credit (after I had flown the rebooked flight) it was granted with no argument or discussion. This lead to me believe that it was completely SOP.
Also, my understanding of original routing credit is that you get credit for the flights as they were originally scheduled, including the dates and times. They will post after the promotional period is over, but that in itself is not uncommon -- partner flights can take a week or longer to post, and even AS metal flights can take a day or two. This doesn't matter; credit is backdated to the date of the flight. I believe that the flights that got me to my final status levels for both 2018 and 2019 we're taken very late in the year and did not post until after the new year, but I still got the status.
Again, I'm not an expert here, as my experience is limited to exactly one time. There are definitely people who have more experience and knowledge than I do; hopefully they will chime in. I can only say that I believe that if you fly the rescheduled flights and then call customer service to request original routing credit, you'll be fine.