> It's called a directory copy. Cut + paste. I'd add a tag with a comment pointing to the old repo (if needed). But probably after a few weeks, no one is going to look at the old repo.

Not in my experience. I use "git blame" all the time, and routinely read through commits from many years ago in order to understand why a particular method works the way it does.

Luckily, there are many tools for merging git repos into each other while preserving history. It's not as simple as copy and paste, but it's worth the extra efford.