I have source I wrote using SCCS as version control, which later was moved to CVS, preserving the commits as well as commit dates, and at some point moved to Git, again preserving commits and dates. So some of my personal Git repositories have commit entries going back to the late eighties.

For any ordinary commit you can simply include "--date=" with the 'git commit' command, e.g. -m "This is an old change" --date="2001-03-02 18:05:47"

I have definitely not done this to fake TDD-ordered commits. Nope not me.