To be honest, this news has made me say: “way to go MS devs” for the first time in my life!
In short, this is what they said (copy/paste):
OS Beta: Updating from 7712 to RTM
Developers can now update their devices to Windows Phone 7.5 without having to
fall back to the backup taken at the beginning of the provisioning process.
This update is being made available to those running build 7712 on a retail
device that was updated using the provisioning tool we published to Connect a
couple months ago.
Have a nice upgrade! 😀