So we know that they have a record of every query that Alexa has detected. I'm guessing what you're questioning is whether they're storing the actual voices so that they can differentiate between different people that have queried Alexa.

I'm quite confident that they store the voice data. It's very valuable to them as a source of training data for future versions of 'Alexa'-like products.

Definitely, as well as being able to eventually differentiate between mom, dad, and the kids.

you know because they let you access and replay the recordings from their app.

But we don't know that's every recording that they have. They very well could have a "allow_user_to_see_recording" toggle.

No, from day one people have been sniffing Echo traffic to see if it sends any non-triggered data. It does not.

I'm thinking more along the lines of;

"Hey we allow you to delete past recordings associated with your account and as far as you are concerned they will be, but we're gonna keep a copy for ourselves right over here, that you'll never know about."

Wow, so they set up the software to guarantee every user is running the same software? and that can't ever get updated? that's pretty amazing.

/sarcasm

Yes, they are storing it. Source: Amazon web site and Alexa app (which let you review / listen do / delete said audio). They are very up-front about this.