>IRC had these archives so repeat questions had a corpus to search
It did? I used IRC pretty frequently back in the day, and the only logging I ever saw was through your own client. This was in the days of dialup, so you'd miss any conversations from when you weren't logged in. If you were fancy, you'd have a bouncer set up on an always-on remote server to log messages when you were away. But I never saw any centralized logging à la Slack/Teams/Mattermost. It's certainly not something supported by any IRCd I'm aware of. Maybe a few channels had custom bots that logged everything to a centrally searchable location, but I never saw such a thing.
Indeed, some here even tout the "ephemeral nature of IRC as a feature, not a bug." [0]
[0] https://news.ycombinator.com/item?id=32000415