Hello Rusty -
Find myself in the same situation and its driving me insane as there is so much conflicting information online - just wondering what you ended up doing?
I contacted apple support too and they reponsded with the same message - so my understanding from that is that actually we can leave Part III - Tax Treaty section (14 and 15) empty/unchecked...is that what you did? Additionally, leaving 8, 9b and 10 section also empty
Any advice would be greatly appreciated :-)