postmortems, do you write one when traffic falls off a cliff?

we lost 38 percent of organic in about four days back in february and the thing that cost us time was not the fix, it was that nobody had written down what happened the last two times. i had a vague memory of a robots file and a staging password. this time i wrote it up properly and it is a page in our wiki now with a fixed shape.

what goes in it: the date the numbers moved, not the date someone noticed, because those were nine days apart for us. every deploy, plugin change, dns change and content change in the 72 hours before that date. what the drop looked like by segment, so was it all pages or one template, one country or everywhere, humans or did the bot number move too. the last one saved me in february, because half the drop was a crawler that stopped coming and had been counted as a human all along.

the fix goes in last and it is the shortest part. the bit i keep getting wrong is timing. i want to write it while it hurts, and while it hurts i am busy, so it gets written a week later when i have already forgoten the order things happened in. i have started pasting timestamps into a scratch file while im working and tidying it up after. does anyone here keep a proper incident log for traffic, or is it all in your head like mine was?