If the album has different title, but is the same of others you may add it in the same release group and, eventually, rename the release group to match the most common title.
Same album is basically same tracklist. It often happens, for example, an album is released with title “Super Album” and later re-released with bonus tracks, under the same name or under another name (which can be “Super Album” “Super Album Deluxe” or “Completly Different Title”), with similar cover art or totally different one.
Whether they fit in the same release group or not is mainly a matter of taste and logic. It is pretty obvious in most cases, much less in some others.
For example, an artist may release an album under one title, then re-release the same exact album under a different title because … well, artists… in this case, we usually re-use the same release group, as we do when it is the same album with extra tracks, but we don’t in other cases: release is an EP, and later an album is released with tracks in common with the EP but added tracks.
We have many different cases, and whether releases share the same release group isn’t always obvious:
Image an artist releasing an EP with 4 tracks, and then later release an album with 8 tracks including this EP, we usually create 2 release groups, eventually with the same title, one being “album” and the other “EP”.
But now, the artist re-releases the EP with 4 bonus tracks (ie. 4 remix of the first 4 tracks): they should usually share the same release group.
In your case, in doubt, just add the release in a different release group, that will be merged later eventually.
Add a note about the similarity in Annotation.