Overwriting multivalue tags in mp4

The mutagen python library https://mutagen.readthedocs.io/en/latest/index.html takes a slightly different view to mp3tag as to how multivalue tags are stored. mutagen adds extra data atoms under a single mean and name (or name), mp3tag creates a separate mean and name with a single data atom for each value. mp3tag seems to read the data values and use the last one. So, when it writes the tag back to the file only one value is preserved. if mutagen reads a tag with multivalues as written by mp3tag, it sees all values, (and then writes it back in its storage form.)

My understanding is that it isn't easy to definitive about what is the correct way to store mutivalues. Could mp3tag be modified to read tags saved in the structures mutagen uses? I think it would be reasonable to write them back in the format mp3tag uses.

Files like this can be made on windows machines using python, or on linux desktop machines using puddletag which relies on the mutagen library. I can provide sample files with tags if that would help. (With very short audio track, and whatever tags you would like)