The content mirror module will only display either the current or the next revision, you are not able to select previous revisions than the one visible for the readers.
If you publish your child mirror page and change the master, then draft the child to update, revision bars will apply.
The Mirror module always shows the updated content of the module it mirrors. If there is a change in the mirror module 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 parent. This way the manual with the mirror module can sit through multiple revisions of the parent content if needed.
In short: If the manual with the mirror is published timely, then it will have revision bars correctly.