When playing with the Discogs API and the file (\Roaming\Mp3tag\data\sources\Discogs.inc) I have come to like what the Discogs API returns, DISCOGS_MASTER_…
With an added script-block some where under Album:
# ###################################################################
# A L B U M
# ###################################################################
…
### MASTER_ID
outputto "DISCOGS_MASTER_ID"
json_select "master_id"
sayrest
### MASTER_URL
outputto "DISCOGS_MASTER_URL_API"
json_select "master_url"
sayrest
### MASTER_URL
outputto "DISCOGS_MASTER_URL"
json_select "master_url"
replace "api" "www"
replace "masters" "master"
sayrest
the Album result now shows DISCOGS_MASTER_INFO, which I sometimes find difficult to find on the website, when looking at release information.
Let me know if I missed something.
Hope this helps.