They are fixed on the events entries but not on the characters entries.
FFXIII Datalogs aren't lying to you, they just aren't giving away the entire story from the very begining. What would be the point in playing it if the Datalog told you everything straight away?
There are situations were it told the exact opposite of it said earlier.
So when you finish the game you can´t really trust it completely.
It´s like the tv news.You can´t trust it until you investigate the reports.It´s reports are constantly actualizing and giving the information "at the moment".

The storyline must be deduced from the character behavior and graphical details.Is is always open ended and logic must be applied.

Registry don´t validate storyline.