That sounds reasonable. I've heard that Willow or Hazelwood(whatever that is) is most desirable charcoal while balsa wood is really good. Ive also seen posts that claim modern black powder is more corrosive because the Potassium nitrate is derived from ammonium nitrate and containes more corrosive salts. I asked the guy in Clarksville about this and he had not heard any thing about it. I'm in no position to evaluate because regardless of propellant, I clean the things thoroughly after shooting.
I have heard claims that 19th century black powder was more energetic than more modern batches. No idea about this but I just read one feasible piece of epistemology that might account for it. Guy posts that only Swiss can be used to gain perfect regulation with traditional charge weights in double rifles- indicating that the rifles were originally regulated with powder more energetic than goex, elephant, etc.
I also have seen a post on another board from an individual who believes that I must have gotten a "weak" or aged can of Swiss because the velocities are so low. I haven't shot enough of it to fully respond to that. I do know that the powder is of recent manufacture and sealed and, since it is producing far more velocity than Goex, I doubt that his response is based on personal observations.