Hi Paul,
The way our system works, if you update a MIB, the user will have to redownload the entire issue in order to see the revised content as we do not support partial updating in that manner.
Please note that for iOS, users will get prompted that there is an update to an issue and they can choose whether to continue to read the current version or update to the newer one.
However, with Android, there is no automated update mechanism so users will have to delete the issue and redownload in order to get the updated content on their device.