I believe the differences found in loading manuals is due to lot to lot variation. Powders are blended, and according to Accurate Arms, the industry standard was 10%. So as long as the blended lot ended up being within 10% of the mean, that lot was shipped.
Back in 1982 (I think) H4350 was advertized as being identical to IMR 4350. Well I have one lot and it takes one grain more powder to get the same velocities as IMR 4350. One grain is not much powder when you think about it.
When Accurate Arms introduced AA4350, I called and they told me it was a ballistic copy of IMR 4350.
I have a lot a AA4350 and can't tell much of a difference across the screens.
These powders have the same long sticks and shoot about the same.
Of course manufacturers can change the mix any time they want, so follow the loading data from the manufacturer at the time of purchase.
And buy by price.