Git rebase: duplicated commits overwrite original commits

Hello!

Here is the situation. Some of my coworkers are breaking the golden rule of git: they are rebasing public branches.

They change the hashes of public commits and do a force update.

As a result, we have dozens of duplicate commits.

I told them to stop doing that because duplicated commits may overwrite the original commits.

But they asked me to prove that. Otherwise, they will keep breaking the golden rule. But I do not know how to detect such overwritten commits among the big mess that we have in the repository.

Is there any kind of diagnosis tool for git so that it can tell you which commits are overwritten because of other duplicated commits?

Thank you so much!