I have signed up for Amazon HD music, I read the SONOS article saying 

What is Amazon Music on Sonos?
There are four tiers of access to Amazon Music on Sonos:

• Amazon Music Unlimited
• Amazon Music HD
• Prime Music
• Amazon Music Library

Ok..  sounds good - but when you add Amazon Music and select from the services it only shows Amazon Music. There is no distinction specifying the different services.

Does the stream revert to what I have purchased “HD” automatically?

Thanks