I have had a further, final response from customer service, which appears definitive, but doesn't address the discrepancy between this answer and the information given in 2012.
Spoiler:
Hello,
Please be assured that we understand your concern. I have reviewed our previous correspondence and your account.
Please understand that the information provided in our last message correctly represents our policy at this time.
As my colleague previously mentioned, Once your account is closed, it's no longer accessible by you or anyone else. You won't be able to access your order history or print a proof of purchase or an invoice. Additionally, the following will no longer be available to you:
* your Amazon.co.uk Marketplace account
* your accounts at Amazon.com, Amazon.de, Amazon.fr, Amazon.it, Amazon.es, Amazon.ca or Amazon.com.br
* your Wish List, or About You page
* your Amazon.co.uk Associates account
* your Author account
* your Kindle library
* your Amazon Music account
* your Amazon Appstore purchases
* your Cloud Drive account
* your Audible.co.uk account
* your Amazon Local account
* your Amazon Video account
* your Public Profile including your reviews, discussion posts and customer images
Further, data Protection guidelines prevent us from commenting on customer or order information that is not related to your account.
Aside from what is available on our Amazon.co.uk, we are not able to provide any further material.
I regret that we haven't been able to address your concerns to your satisfaction.
We won't be able to provide further assistance for your request.
Warmest regards,
Ethiraj D.
Amazon.co.uk
Your feedback is helping us build Earth's Most Customer-Centric Company.
I think I have no further recourse at Amazon, except the long-shot of an email to Mr Bezos himself.
Assuming that nothing comes of that, I think my next step will be to approach some of the journalists who cover the 2012 story.