[DaveBlake]

As for your second suggestion regarding the sorting by release type I was searching for the Release Type or something like that in the Node Editor, and have totally skipped just the Type tag.

There is room for confusion here because of naming of tags (embedded in music files), xml tags (seen in nfo files) and field names in music db (if you start poking about in there). It is unfortunate, but there you are. To try to clarify it is easilest to start with the db.

The album table in the db has a strType field that can hold anything the user wants, and a strReleaseType field  that is used internally and must not be modified. The strType field is the value used as a filter for the "type" rule in "albums" smart playtlists.

Both these values are exported into album.nfo files as <type> and <releasetype> respectively. Users can set <type> to something and it is applied to change the db value when the nfo file is scraped, changes to <releasetype> make no effect internally to Kodi.

There is a tag, provided by Picard but other tagging software could also add this, called "release type" in the Picard UI and written as metadata to the following named tags in the various formats:
TXXX:MusicBrainz Album Type,
RELEASETYPE
MUSICBRAINZ_ALBUMTYPE
----:com.apple.iTunes:MusicBrainz Album Type
MusicBrainz/Album Type

The values in this tag end up in the strType field of the db taken from the first song of the album.

It would have been better if Musicbrainz had been consistent with their tag names, Kodi could also have avoided calling an internal field "strReleaseType" given the possible tags confusion,  but stuff like that happens.

So once again documented for posterity, and maybe a useful reference for someone searching in the future.

Enter album type values (via a music file tag somethings called "RELEASETYPE", or <type> xml tag in album.nfo files),  and filter on them in any ways that are meaningful to you .