They may have tried. Most of the services used to wipe posts and comments were ineffective on content more than a couple years old because Reddit wouldn't report that the content existed.
I couldn't verify this directly either, but I know some users had also claimed that, after Reddit started catching on to what people were doing, they'd keep the content anyways, un-edited, and just hide it from view on your account so you wouldn't know it was still there unless you went back to find the original posts, which most people wouldn't know where to find.
During the whole debacle, I wiped my content but kept my account in the hopes that they'd backtrack on their decisions. Shortly after joining Lemmy, I googled a question on Reddit and saw that I had an inbox message, someone replying to a comment that I had made years before which, surprise, was not deleted. Clicking on my comment history on my profile showed nothing, but the message was still there in the thread under my name.
I used some script some dude made back then, changed all the text "if you can read this, Spez did not only fuck up reddit, but also performed vasectomy on my old account and revived this comment, which used to be meaningful“
I'd be surprised if that's still what it says. They have the edit history, they could roll it back whenever.
I guarantee with 100% certainty that that isn't what they're feeding into their AI, as well. You just planted a great big flagpole on all your old content that states "this account was previously run by a real live human" and probably doubled the value of the edited comments for AI training. Bots don't have a reason to protest-edit their content.
I approve of the attitude, but spez has got us in a vice here where any attempt to damage reddit's data store is actually just helping them. Best thing to do at this point is to scrub them from memory and just ignore them forever. Unless you're up for some seriously large-scale corporate sabotage, that's the best we've got.