Default Office 2000 files with old data in Office 2013

I'm really wracking my brain here trying to figure out this problem. A business that do support for recently upgraded both from cheap windows 8 to 8.1 and Office 2000 to 2013 (365) on a new PC.

Among the secretaries had documents in what is now a protected folder in Windows (C:Program FilesXXXXXX) etc. These files opened fine with Office 2000 (still installed), however when opened within the 2013 iteration, these were missing data going back to some time.

The only real silly workaround I have been in a position to discover thus far is to open the file in Office 2000 after which save it for an unprotected folder such as (Mydocuments or Desktop) etc. Opening it in Office 2013 shows the correct data. Whether or not the file is then copied to the protected folder and overwrites the initial, after that it works fine. I can not just copy the files out, they need to be saved individually.

I've even tried modifying the permissions to TakeOwnership of the protected directory structure and also the files still open with old data.

Office documents should never be saved to the folder under C:Program Files. Those folders are for programs, not user data. Perhaps you have tried simply copying/moving the user files from C:Program Files towards the user's Documents folder, then opening them after that?

I would include the different results you're getting with cheap windows 10 pro and Office 2000 suggests you're actually opening different versions from the files.