One data source i've been thinking about that i don't know if they've hit yet is all the different agencies local and state agencies and their private and public meetings, ordinances, discourse, etc...
And it’s going to get worse I now that paper files are disappearing.
I wanted some info and data from a test we did 9 years ago. It was a pretty big deal, lots of people involved, many millions of dollars, multiple nasa centers contributing. Every single person on the test randomly kept their own files for the portion of the test they were responsible for. And the only copy of the raw test data was deleted by one of them to save some space when upgrading. There is no record anywhere of what equipment was used for the test.
One of my coworkers has 4 TB external HDD that he keeps everything he has ever worked on. It’s not backed up anywhere else. It just failed and he thought he lost everything, luckily I was able to recover most of it. Wtf.