Then there's the portrayal of the tragedy on Arvada III which if I recall is inconsistent with the previous way it is referred to by Vaughn in Avatar.
And after checking Memory Beta, yeah... Vaughn bore witness to a genocidal holocaust on Arvada III while DiW established the tragedy as a plague outbreak.
Not entirely implausible that it could be fixed into one event, but there's no attempt thus far that I've seen, and they don't seem to be talking about the same event when read side by side.
They could easily have been two different events. I mean, why assume there can be only one tragedy in the entire history of a given planet? How many tragedies has Earth suffered in the last eight years alone? Avatar
doesn't specify the date of the genocide on Arvada III, so there's no reason to assume it's the same event.