I commented on the edit, but this should not be merged - the recording guidelines specify that. One thing that isn’t too clear by the choice of the word “recording” is that a recording in MusicBrainz is more like a “mix” or “edit”, rather than just the result of the actual act of recording something. These should be linked to the original with the edit relationship.
These are also separate recordings according to the previous definitions. However, since the combination of the two parts equals the longer one, it’s better to use the compilation relationship for these.
That said, I agree that we could use a good way to copy all the relationships from one recording to another for cases like this. I’m not sure if there’s already a userscript for this purpose.