You said with certainty, as a fact, that HP38 and 231 are the same powder. But that statement as it applies to using manuals neglects that the powders were not always the same. Therefore, the data could be used with older batches of powder but not with newer cans. IMO It only requires a warning about powder changes, not an indictment of the entire manual based on one factoid.I can't say that i understand your statement.
I can see why the company would say it, but I haven't seen similar statements from any other publisher regarding using their older books. Maybe I missed it... are you aware of any other publisher that has made a statement saying not to use their older books?