Aelius Herodian was a grammarian who lived in the 2d century CE during the era of Marcus Aurelius. He is the ultimate source of much of the information we have about ancient Greek accentuation (and perhaps some misinformation, too).http://en.wikipedia.org/wiki/Aelius_Herodianus
See Probert, A New Short Guide to the Accentuation of Ancient Greek
, secs. 21-2, pp. 13-14.
Herodian wrote several treatises on accents, which are lost but are known through an epitome written around 400 attributed to Arcadius or Theodosius, some later Byzantine grammarians, and the A scholia to the Iliad (those found in the Venetus A ms.), which are believed to incorporate material from a commentary that drew on his work among that of others (the so-called Viermännerkommentar, or VMK, "four-man commentary"; Herodian was one of the four men).
So our information about Greek accents has come down through the ms. tradition, as well as in grammatical works and scholia derived from Herodian. I'm sure some inaccuracies and misconceptions must have crept into this material, especially about very minor points, especially since the first-hand material we have dates from the era after the tone accentuation of ancient Greek had given way to a stress accent. And there are some disputed topics, too.
Addendum: you might find this Wikipedia article on the Venetus A ms. interesting:http://en.wikipedia.org/wiki/Venetus_A
Note that Erbse derives the material in the A scholia from the VMK through several intermediate stages.
Homeric scholarship is a bottomless well.