That only applies when the target was relatively anonymous to begin with. It's frowned upon to crawl back in time to look for ammunition against someone, but if

That only applies when the target was relatively anonymous to begin with. It's frowned upon to crawl back in time to look for ammunition against someone, but if that ammunition is something that went viral and is part of public consciousness, then you're good. One example is Bredan Eich. Because he chose to donate to a Prop 8 fund and it got out, his opinion on all subjects is automatically null and void for many people. Another case is that of reddit user 'Unidan', who became an immediate pariah overnight because he was a dick to someone online, so he abandoned the entire identity. If any of his alternate identities were somehow linked back, it would likely become useless as well. I'd be willing to be his professional career suffered greatly because of that rant, too. There's also Joy Reid, who has been in hot water lately because people found old tweets and blog posts that were offensive. In that case, people actively went back to look for things she said in the past. None of these would have been possible pre-internet.