As far as RL-19 is concerned and this is true with any powder, as long as your load is not boarding the max that your rifle will withstand with a given charge and it is an optimal charge weight, you may never see a difference from one lot of powder to the next. However, if the load is not an optimal charge you should expect that there will be a difference from one lot to the next. The best advice you received was to purchase a bulk "8 lbs" of powder or more and check the load with the new lot to confirm and adjust it if need be. The "optimal charge" will be a charge that even if the weight were to change by +/- 2/10ths of a grain, the POI would not be effected. By concentrating on a OCW, I was able to come up with three loads in my 7MM using RL-19, RL-22, & IMR4831 once I found the harmonic velocity "sweet spot" that rifle liked. This can be done in any rifle if one wants to spend the time.
On another note and I don't mean to be a killjoy!
IMO FWIW, load data from one rifle usually never translates to another. Even if the rifles were made in consecutive order. Accuracy is dependent on harmonics timing and barrel wip among other factors. The chances of two rifles having the very same stocks, bedding, scope & rings, timing can be altered greatly by how the stock is torked as well as other accessories. Climate and altitude also makes a big difference. As long as you have data from a reliable source with documented min & max charges to start with, that is what you should be working with and nothing else. Not saying it is impossible but highly unlikely.
If one is only asking what another reloader is using to compare against what they find to work in their firearm, that is on thing. But if someone is asking so they can try it in their own firearm, I highly recommend they change their reloading practices and put safety as their primary concern before anything else.
I only say this because I've seen what happens first hand when you don't and it was a real eye opener!
Sorry.
