Sorry I don't understand what you mean? I made the custom tag "trackyear" and it doesn't show up anywhere. How is this different than what I am doing above?
You have to tell it to show up, right click on the headings at the top of the main view and you can select which fields show.
The way it's different is that the track now has two date tags, the date of release of the album it's on and the date of release of the track itself.