You could potentially see a more consistent STD between rounds in the same lot vs comparing multiple lots if the QC is off.
Because everything can change in between lots. Different brass, different primers, different powder. Even within the exact same brand and series of ammo.
I will give you an example. My brother recently sighted in his 6.5 PRC with Hornady outfitter ammo. 130 gr CX. Because he’s not a detail guy, and never listens to anybody about anything, and incredibly cheap. He only bought a couple boxes of this ammo once he found out that his rifle shot it well. Of course he soon ran out of just those two boxes and went to the store to buy more a few months later. Same Hornady outfitter, 130 gr CX. This lot was 300 FPS slower. Yes, that much.
Component shortages affect manufacturers too. They have a hard time keeping everything the same these days. And by necessity may have to change powders or something else important. It’s been widely broadcast recently.
So once you find what ammo your gun likes, you need to make sure you have a long-term supply of that same ammo, from that same lot, or you will be constantly sighting in again, and having to calculate your drops with new dope.
Also, do not listen to what anyone else says worked well or work poorly in their gun. Even the same make and model as yours. All guns and barrels have their own unique personalities that will respond to different ammo types quite differently. You need to find what your individual gun likes and the only way to do that is to try Several different types.