I came across today one of my own comments on Reddit with a search on duckduckgo. It was still intact. The problem is I used shreddit to randomise and delete the entire contents of my account. My account comments and posts all show empty on my account pages on reddit so there should be nothing.
I did a site:reddit.com search using my username and found ~50 comments that Reddit has undeleted but also hide from my own account. I could still edit and delete them. Its curious that they don’t appear on my accounts content on Reddit and yet a search engine can find them and they are still served by Reddit. Ex Reddit users who deleted their account contents should be aware this is happening and report it as a GDPR breach to their respective agencies if they are in the EU if they too find this has occurred.
The fact that they are too old to show up in your profile is WHY it can’t delete them. The only way to delete those automatically is to feed in a GDPR data request into a tool like Shreddit that supports getting its comment list from that source rather than the profile.
OP of this post said they used Shreddit
You need to specifically use a GDPR export with shreddit though, it’s not magic, and if you don’t have a GDPR export, it can’t get around the 1000 post limit on the profile.