You posted a lot of good data on this event - but I don't remember, was there an online source?
Could you provide whatever you have?
I don't believe there was anything nefarious behind Berthier's passing, but then, who would have guessed Soult was a traitor! :)
Did anyone in 1815, or did any of Berthier's peers ever suspect anything? Or are the various theories of recent creation? (see Hamilton-Williams theories involving Artois and/or the Knights of the Faith or whatever their name was... which was a real organization, and despite a few publications by ancestors, remains shrouded in mystery)
(And don't forget the Rosicrucians - who saved Ney and brought him to America - its all in their records... half tempted to join just to see this through... maybe I'll meet Tom Cruise.)