Referring-domain totals come from the public Common Crawl graph (full page/anchor index like Ahrefs is paid-only). Linking pages and anchor texts below are a live web sample.
redis.g/404;mc.g/404;rs40_shard.sel:4/not found;rdb.g/no such key;DBD/404;v4.get/Document not found;rwro.get:4/Document not found;RS.dbs:4/Document not found;RS:4/404;redis.g;2s.gh;PFDS;IO:14