I have a paid Slack plan and while I can find specific threads where I remember a lot of the details, I've never found anything that I didn't personally participate in.
Overall, I think search is a bad knowledge base management tool. It proves the positive quickly (search for "foo", see "here's how to use foo"), but never lets you prove the absence of documentation (search for "foobar", nothing comes up, search for "foo bar", nothing comes up, search for the previous codename "barbaz", nothing comes up... did you forget something, or is there just no documentation/discussion? you'll never know. the result is that people stop reading documentation.)
Overall, I think search is a bad knowledge base management tool. It proves the positive quickly (search for "foo", see "here's how to use foo"), but never lets you prove the absence of documentation (search for "foobar", nothing comes up, search for "foo bar", nothing comes up, search for the previous codename "barbaz", nothing comes up... did you forget something, or is there just no documentation/discussion? you'll never know. the result is that people stop reading documentation.)