What I know now is that you can just use the --committer-date-is-author-date
with a range of all dirty commits after a rebase session that reset a lot of dates.
The above seems to not always work. When in doubt:
git -c rebase.instructionFormat='%s%nexec GIT_COMMITTER_DATE="%cD" git commit --amend --no-edit --allow-empty --allow-empty-message' rebase -i HEAD~N