I just scribble down whatever seems important as I'm playing, sometimes go back to match reports for detail, but in the only story I've written so far the narrative is much more important than what goes on in the game, which is why the story is progressing so slowly in terms of 'game dates'. Actually, another reason for that is I don't really have much time to play CM solo, especially now I'm writing about it, so I tend to mix up actual game occurrences with a lot of background or 'peripheral' features, which don't require having to play the game in a sustained manner.
'Whatever you think is the most fun' is probably the best rule to apply here -flogging a dead horse simply to avoid being branded a 'quitter' (or a 'story whore'...

) can only result in disappointment and frustration, both for you and for the readers following the story.