Okay so I'm willing to put this to the test, for Express and Standard at least. When I submitted my first EX it was a 15 day TAT that got lowered to 11. On day 10, I was scheduled for grading and the TAT went up to 22 day. On day 12, it was shipped back. I still have one standard order that was received when the TAT was 25 days, and an express that was received when TAT was 11. If stuff is getting "grandfathered" in, My express should be in grading by the 25th and my standard by the 31st.
This is assuming all runs according to plan though, and I'm not holding my breath for that haha.