One issue that I didn’t see addressed in here anywhere is field dominance.
If the destination is NTSC broadcast wouldn’t you have to account for the HD odd field dom vs the NTSC even?
I had fits with artifacts and jagged image edges a few times on account of this. I have also had some issues with projects exported out of Avid Media composer with no dominance. Seemed like the combination of FCP, compressor and going out SD via my AJA did something different every time 😉