This appears to be related to users modifying the contents of the Microsoft Office folder in ways which do not cause problems with most other software (such as "localizing" using a program to remove application support files in unwanted languages), and which do not affect Office's operations, but which cause the updaters' installers to believe that the application is not valid for update.
It appears that users are modifying the Microsoft Office folder in ways that do not disrupt most other software applications, such as customizing localization using a program to remove unnecessary language files. However, these modifications lead the updaters' installers to incorrectly assume that the application is no longer valid for update.