While you personally may already know this, and this doesn't solve all problems; be sure to look for and read the tiny little mostly-greyed-out link to the search syntax for Slack: https://get.slack.help/hc/en-us/articles/202528808-Search-in... , in particular the "Use search modifiers" section. Slack defaults to a nearly-useless search if you don't feed it things like a channel limitation or something.
Also, do you end up extracting conversations into docs, or something that's easier to share with your team?