4chan archives are almost certainly relevant. But the advertisement poster for every single club night in Berlin probably is not - a representative sample is enough. More complete data is probably more useful, at least slightly, but it quickly runs into diminishing returns. The distinction is that certain 4chan posts have outsized influence (power law distribution of influence?), but club nights are all the same. It is conceivable that a certain poster could be important and not recognized as important in the moment, but not as likely.

And that's public announcements. Do we really need to archive more than a few of the "I'm in this city, look at me I'm so rich and beautiful" short videos?