I moved our conversation into a new topic, as we are getting more and more off-topic from the original thread.
That’s true, the plugin could be changed to get the ASIN anyway. Currently it depends on this, because it is using the URL relationship of type “amazon asin” on the release. I think the ASIN being returned as an attribute of the release entity did come later.
I wonder what happens if there are multiple Amazon links on a single release? Shouldn’t happen, but I have definitely seen these cases.
Just for other to see what we are talking about, the following web service request shows the ASIN both as an URL on the relationships, but also there is an asin attribute:
https://musicbrainz.org/ws/2/release/0a606073-cc75-3940-a52d-0823f0c4f06e?inc=url-rels&fmt=json