I did have (Store in file tags) option enabled.
MC has the global option in "Options > General > Update tags when file info changes" and in addition each field has a separate option in "Options > Library & Folders > Standard/User Fields > [Field name] > Edit this field > Store in file tags (when possible)". I hope you had both options ticked.
If the field values are stored in the file tags it is possible to recreate the field and update data from the files.
Would you explain how I can do this please?
You would need to recreate the field and do "Library Tools > Update Library (from tags)"
You could check the "format info" and try to find a field that contains your review data. Here's how you can access the format display:
You could right-click copy the detailed format info to clipboard and post it here.
Did you only have the automatic library backup files in the default location? No backup copies in some other safe location?
YES!!!
You really should consider of backing up all essential data on a second hard drive. Besides that an user or software error may occur a hard drive is likely to crash - sooner or later.
If you enabled the "Remove Media Center 12 library files. (For complete uninstall only. Do not check if upgrading.)" uninstall option the uninstaller deleted all MC12 related files in your user profile specific application data location including all automatic backup files.
The other issue of my Library Backups being deleted when I have done this before without ever effecting my Backups amazes me. I had no idea this would happen. Is this common knowledge? I had thousands of songs catalogued on MP3's and the data of them has completely disappeared.
Maybe you didn't have the "Remove library files" option ticked. AFAIK, its behavior has not changed.
In general, I'd recommend periodically saving a manual backup file to some other drive. The automatic backup files may not contain all recent changes if something unexpected happens to the library. Personally, I run the backup tool before and after any big changes (I give the files unique names if they are from the same date). Usually I have about 10 to 15 recent backup files in a safe location.