[knc1]

Now put one of the Amazon end-user update packages on your exported USB drive and then re-boot (the greater than 20 second thingy).

From the serial line (at the point where you could enter the 'dd' command) enter:
cat /etc/version
cat /etc/pretty-version

That will tell you which device (pw1 or pw2) and which firmware you now have on it.
Which in turn will tell you which Amazon update package to grab.

The re-boot process should recognize the Amazon update package, install it, and that will "un-demo" the device for you.

- - - -

Welcome to the forum -
you made a lot of progress on your own.