GI1 yes, clearly easier. I literally went to the release page, ctrl+f pixel 8, reverse searched (shift+enter) for the very first entry in the changelog and found the release 2023102300 with "initial non-experimental release for Pixel 8 and Pixel 8 Pro support"
That means the first GOS p8 release was 23. october 2023, and the p8 released on 12. October 2023.
Now you can do the same easy search for the p9. Then add another month on top for the p10 because that'll be harder to port, now that google doesn't release the device trees anymore.