But, wouldn't that require much more than just an additional tag field?
To get it useful, a filed would need to be added, additions is need to be made to the tag editor, it needs to be added to the advanced search and also probably somewhere into the custom view, so that you can track which releases that you are missing. Isn't that correct?
Personally, I use the part of series tag field (which is available in the custom view) to track missing releases.
I collect for example react cd's which are labled in the way you describe, as well as other "series" such as rave mission, rave now, trancemaster, gemini project etc.

