Not all post-mortems are for failures/dead products which might add even more confusion. For instance Gamasutra runs a game development post-mortem section where developers of popular (and unpopular) games can hop on and describe difficult situations they've encountered, how they did what they did, why they did that thing, etc.
It's really fun to read.
http://www.gamasutra.com/features/postmortem/
edit: Wow, there hasn't been one since 2014. I wonder why this died out. There's 10 pages of them since 2007..
Re:Google Cloud Downtime Postmortem
by s_ngularity on Thursday July 19, 2018 @09:04PM
(#17571691)
Ironic. Apparently we need a postmortem postmortem
It might make a little more sense in the world of shipping software in retail boxes, where products/projects had a 'done' date. The project is dead, what contributed to it's demise? Or you might generalize death into failure, and that's why we use the term instead of post-incident.