As was raised by markn in the developer chat (https://t.me/moodledev/82900) and in the forum (https://moodle.org/mod/forum/discuss.php?d=417684), the Git repository of the Certificate manager started by copying Mark's code (https://github.com/moodleworkplace/moodle-tool_certificate/commit/0acb3f4864df9f1878e954e00e26a4969fc1bfd9) instead of forking it.

As a result, all the history of Mark's commits was lost so Git commands like git-annotate do not provide right information. Mark is also not mentioned at https://github.com/moodleworkplace/moodle-tool_certificate/graphs/contributors and other places where the commits authorship is used.

Even though this is not a violation of GNU/GPL (as Mark's copyright statements remained untouched in all files etc), this was not optimal way to start work on top of someone else's project.

I believe this can be still fixed by rewriting the plugin repository and rebasing it on an appropriate commit in the original Mark's project.