I guess some of you have started to figure this out, but just to be clear as there seems to be some confusion.
The SBK is chosen by the manufacturer.
Acer have choosen to (for some of their models) base the SBK on the UID. This does not neccessarilly mean that this is the way it is for any for any devices by any other manufacturer, or even for other models from Acer. It could be that they have chosen to do it the same way, but it is highly unlikely.