That graph has bugged me since it went viral. The methodology is horseshit: https://github.com/DaMrNelson/github-historical-uptime

Just dumping HARs from devtools from a status site that hallucinates 100% uptime when it has no data. For example, all GitHub services had 100% uptime in June 1996: https://www.githubstatus.com/uptime?page=200

The graph gives GitHub Actions 100% uptime before it launched to GA in November 2019. That factors into the average uptime for every month on the graph before that. It's fully horseshit.