Just a note on your nr1: I don't think rebase back-dates the CommitDate, does it? There are two dates on any commit: AuthorDate and CommitDate. Try git log --format=fuller. E.g.:

    Author:     ...
    AuthorDate: Wed Aug 2 11:02:03 2017 +0100
    Commit:     ...
    CommitDate: Wed Aug 9 12:08:52 2017 +0100

This is a commit I originally created last week, but rebased onto my current branch just now. To change the CommitDate, you have to go filter-branch, afaik. But maybe I'm ignorant of a germane rebase feature?