What you are seeing it the Lot-to-Lot# variation. Making the powder is a very complex operation with many possible variables. Some powders seem to be inclined to greater lot# variance, especially the spherical or "ball" type powders.
I've shot more Win231/HP-38 and Bullseye than any other powders. I've seen as much as 5% variation in density/energetics/velocity/pressure with the extruded type powders (ie:Bullseye- a "flake" type extruded powder). However, with Win231/HP38, I've seen variations greater than 10% regarding the aforementioned criteria.
One batch of Win231 I aquired and exhausted in the mid-late 90's was exceptional regarding accuracy. I won numerous matches, and tied or established several National records in NRA PPC with that "batch". After it was gone, my averages took a noticeable "dive" and I haven't been able to duplicate the results since. However, the Bullseye I use now, occasionally approaches the performance of that single lot# of Win231.
So, even it the powders are the same (they are), you'll still see the published data difference due to different lot#'s. This is why all the manuals state that anytime you change ANY component, even Lot#'s, you should rework the data. Kinda of an extream precaution, one I frequently ignore with my match level pistol/revolver loads, but a valid precaution nevertheless.
Want talk about some differences in rifle loads?, try some BL-C2 manuf'd in late 70's and compare with some made last year !!!!! (Hint, as much as a 10% difference in max. loads with ALL other components and rifle the same). The latest lot# is VERY much slower burning and hence higher charge weights, and higher velocities than the previous lot. Also, note that the max recommended charge weights on Win760/H414 are as much as 5% higher than they used to be. IE: Hodgdon used to recommend 58.0gr as max with a 150gr .308 bullet in .30/06. Then, it went to 60gr, now it's at 61.0gr.
Quite a difference when we are talking old CUP data vs. current PSI data which has caused most other power/data to go in the opposite direction(reduced charge weights and velocities).