The Pictish Chronicle is not a dated list of events (as with the Anglo-Saxon Chronicle) but rather it is a list of the kings of the Picts giving the duration of each reign. Starting with the mythological Gud or Gede, through to Brude (1) (probably the first historical king in the late sixth century) and ending with Kenneth Mac Alpin.
There exist at least seven versions, (2) the earliest dating from the 970's the latest to 1317. They differ from one another for all the normal reasons such as scribal errors and deliberate modification, but belong to two distinct groups and therefore two original manuscrips probably begun sometime after the arrival of Saint Columba. (3)
The two versions start off with more or less the same list of kings, and end up with more or less the same list of kings, but differ greatly in the middle period. Strongly suggesting a period of dislocation and strife when there were multiple claimants to the throne.
(1) Or Bruide, or Breidei, there are many variations.
(2) First collected together and published by W.F.Skene in Chronicles of the Picts, Chronicles of the Scots and other Early Memorials of Scottish History (1867)
(3) Which since the departure of Columba from Ireland can apparently be reliably dated to 563, means sometime in the late sixth or early seventh centuries.