When a new version of a feed is created in ModeShape the access control to that feed's node tree is frozen as of the state it was in at that point in time. If a user/group is later granted access to that feed it only affects the current feed version. Therefore the user will not be able to view the prior version since it still has the older access control state. I don't believe there is a way to change that frozen state.
The easiest fix I can think of right now is, when viewing a feed's version history, if permission check for read access to the current feed version succeeds then a separate query would be made for the feed's prior versions in a privileged (service) mode that bypasses the access control restrictions.
We may also want to consider having access to a feed's history as a new kind of permission that can be granted.