Adding physical tags to wave files wasn't possible until recently. It was added during the MC14 development cycle.
The feature is not enabled by default because there's no guarantee that the tags would not cause problems with other player programs or hardware player devices. The tags are stored in a way that conforms Microsoft's wave file standard, but most other players do not understand tags in wave files and some may even have playback problems with tagged wave files.
You can enable wave tagging in Tools > Plug-In Manager > Input > Wave & AIFF Plugin > Configure... After the feature is enabled, you can do "Update Tags (from library)".
However, as Jim said, you can always preserve your old library data by restoring a library backup file. In addition to all field values a library backup file contains the playlists, statistics and most if not all of the customized view configuration (schemes, columns, sorting, etc). Some view related things may have changed during the development process and thus may not be preservable.
In the previous MC version: File > Library > Back Up Library...
In the new MC version: File > Library > Restore Library...