Edit Metadata, Add Field for WMP

Using Audacity 2.1.2 (Yes, I know there are updated versions).

In Windows Media Player, I use a few provided fields for specific information about tracks. One of those fields is labeled 'Key". If I manually enter a keyword there, I can use it to sort or select playlists.

I’ll be parsing out a few hundred tracks using Audacity Export Multiple. I don’t want to go back and manually edit that Key field. I just tried a set using Edit Metadata, Add field and entered the keyword I need. It did not populate the field in WMP once the tracks were moved there. Did I miss a step somewhere or is this this not something AUD can do for me?

There is a an add-on called Windows Media Player Plus that’s supposed to add tagging/metadata features but I don’t know if it will display a “key” tag or any custom tags.

Some players may not display all of the standard tags and custom tags are generally not displayed.

And, different audio formats support different fields. I don’t know if “key” is a standard field for any of them. MP3 files use ID3 tags. FLAC uses Vorbis comments. AAC/MP4 uses something else, and metadata for WAV files is not widely supported and it doesn’t seem to be standardized.

The fields I want to use are in WMP by default and display properly in both WMP and the File Explorer. I just want to know if I can populate them in the AUD Edit MetaData screen while Encoding instead of having to edit manually or use another bulk editor.
I tried adding a field in that screen before encoding, but it doesn’t show in either WMP or the File Explorer.