I don't tag my music and I don't want to because the way tags are handled is not uniform across devices/programs. And I never had to. I simply name my files by the "artist - name" pattern and that's all I need.
I don't need browsing by genre, artist, year or whatnot.
However "Recently added" list is convenient. I used it on every played I had. But in Rockbox every song on this list is <Untagged> for me.
My idea would be to show the file name when no tag is found.
"Recently added" feature relies on created/modified metadata so there is no real reason why it has to use ID3 tags to display the name.