You have to enter their marketplace to access what you already have. To get to your free stuff, you are further exposed to the marketing whims of Amazon.

If it's unavailable, I'm quickly reminded that I can upgrade to an Unlimited subscription or I buy the album as an mp3 to add to my Auto-rip collection. I can search for a song or an album and it'll be presented. I use the same app either on my phone or my computer to access these songs. I can't download these, but I can stream them. But I also know that with my Prime membership I get access to a lot of other albums that I don't own. I can stream albums from my car if I want to.

Anything I bought previously was added to mp3 downloadable cache at Amazon. When the program first started, I had about 50 albums in My Albums from Amazon. When the Majors reentered vinyl, they matched the mp3 to remove the indie labels advantage. Buying an indie record gave you some value. This gave them a competitive advantage over the Major labels who weren't even selling much vinyl in the early '00s. It was the indie labels that included these download first.

You could buy the album off iTunes or buy the vinyl album and it included the mp3 files, so the extra cost of the physical media would be offset by the inclusion of the price you would pay had you bought the download alone. I first remember digital downloads included with vinyl when iTunes became a thing. In the case of digital download codes, this was a way of adding some value to vinyl which isn't easily ripped to digital without some additional investment of gear and software. They are enticements to get bring you into to their ecosystem. I tend to think Auto-Rip along with digital download codes are just marketing freebies.

Amazon prime cds