When you invite a user to review a proof, the button in the email takes the user to a new browser tab (outside of the Smartsheet project plan). If more than 1 version exists, you can only roll back to see those versions if accessing the proof from within a project plan to see if corrections were made. The invitee cannot do that as their access only allows them to review the proof in the separate browser tab. Can you make Versions accessible for review from within that separate browser tab?
Also, looks like this has been an issue for years, as seen in this older post below:
https://community.smartsheet.com/discussion/79327/proofing-feature