As I recently learned, Windows Update also forces 1709 on some computers running 1703, when the Atom CPU in those old computers has been specified by Microsoft as incompatible with 1709. Rather than noticing the Atom processor, avoiding 1709, and installing the appropriate updates to 1703, Windows Update keeps trying and failing to install 1709.
I retract post #36. After spending a ridiculous amount of time on it, I finally got 1709 installed. It is not incompatible with all Atom processors, just Clover Trail processors.