The content mirror module will only display either the current or the next revision, you are not able to select previous revisions other than the one visible to the readers.
The Mirror module always shows the updated content of the module it mirrors. If the mirror module changes compared to the previous revision of the page, then the revision bars will be generated on the page. It does not have to pull the revision bars from the template. This way, the manual with the mirror module can sit through multiple revisions of the template content if needed.
If you publish a child document with a mirrored page and change the template, then draft the child to update, revision bars will apply.
In short: If the manual with the mirror is published timely, then it will have revision bars correctly.
Content mirror module and revision bars
Jody Bright
Web Manuals Team