Note, there should be as many historical sightings of the Akaviri men as there are of the Akaviri beasts (if not more for this latter case).
For reference's sake, indulge in reading 2920, The Last Year of the First Era, Morning Star / The Arcturian Heresy / The Story of Lysirius.
As well as Pocket Guide to the Empire, 1st Edition: Cyrodiil/Skyrim and 3rd Edition: The Seat of Sundered Kings, Cyrodiil/Other Lands.
Now add the depiction of snake-like heads on the hilt of Duskfang/Dawnfang (which has similar attributes to the Tsaesci described
in Mysterious Akavir) as well as in the interiors of Fort Pale Pass (to which was home to aptly named hint called the Draconian
Madstone) and you've got a quite convincing viewpoint of Mysterious Akavir being mostly supported in it's claims of fancifulness.