[shamanNS]

I'm not sure if I remember things correctly but I think if you just copy the old firmware bin and disconnect from computer that Kindle will delete that bin file straight away?

So in order to avoid that issues you don't disconnect your Kindle from your computer after you've copied the 5.16.2.1.1. bin file instead while Kindle is still USB connected you press and hold Kindle's power button for 30-40 seconds and that will force a reboot, and on reboot Kindle should start the firmware update procedure... and that will hopefully install successfully.
You should unplug the USB cable when you've triggered a reboot by holding power button.