The Police officers had an old saying that the only difference between a "Fairy Tale" and a Police Officers "War story" is that the Fairy Tale begins "Once Upon a Time" and the Police story begin "This ain't No ----".
So it is all a matter of perspective of who is telling the story. Still all Fables, Stories and Fairy Tales have some basis in fact the trick is in determining just exactly what are the facts and piecing those facts together into a more complete understanding of what was actually going on.
After all the best way to tell a conviencing lie is to use mostly the truth and change only those parts which serve your purpose. In Porters case that purpose was as you say self engrandisement. In writting about Arkansas Post, since he wasn't there, that self engrandisement had to have been "I was an important person duirng the War, Listen too how much I knew about"
Thanks for your perspective on David Porter.