I have a lot of Nimbus Records. They’ll release individual discs such as http://musicbrainz.org/release-group/83e64372-864c-4a51-9ff1-1a75bd2665cb and http://musicbrainz.org/release-group/98dcc1e7-4393-4e2b-ab15-ff98f54f6731 and then later release as a two disc set with a combined catalog number like NI 7713/14.
Is there an easy way to merge these two discs into another single 2-disc release? Should it be a new release group?
Edit: i figured it out, of course. You just add two media and base them on the existing entries.