As Ivan and Alk both pointed out it’s just normal lot to lot variation in canister grade powders intended for reloading.
With data for H110 and Win 296 the folks working up the load data obviously had powder from two different lots. Look across a number of load data manuals showing both in the same table and you’ll see similar variation - up to .5 grains in some handgun loads.
The fact that so many reloaders don’t understand this variation occurs in different lots even in powder with the same label is the second most disturbing thing I see.
Simply put, a max load listed in a load manual is a max load for that particular lot. It’s why you are directed to start 10% below max and work up.
It’s also why if you are loading to a specific velocity you work up a new load with each new batch of powder.
The most disturbing thing I see are reloaders who don’t understand that canister grade powders intended for reloading have much less lot to lot variation than bulk powders used by ammunition manufacturers.
For example, I see folks talking about replicating military loads for things like M1 Ball, M80 Ball, M193 ball etc and they will cite a source for a “nominal load”.
They apparently don’t understand that a nominal load of, for example, 42.6 grains of WC846 doesn’t mean that 42.6 grains of a lot of WC846 will produce the desired 2800 fps velocity. Variation in bulk powders is huge, particularly in WC846 which has always had a very wide specification range. It could easily be 2-3 grs off the “nominal” charge weight.