Yes I know I should know this, but I thought by giving 3 specific examples with well known cities and airlines so it could clear up some of the other threads on Back-To-Back and nested

Suppose I was flying the following and credited all miles to UA.

1)
YVR - HKG (Air Canada)
HKG - SEA (UA)
SEA - HKG (UA)
HKG - YVR (Air Canada)

Note ticket number 2 (UA) is as I understand it back to back because it is between the (Air Canada) ticket. However it departs YVR which is a different airport then SEA. So is this then Back-to-Back or nested?

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2)
SEA - HKG (Air Canada)
HKG - SEA (UA)
SEA - HKG (UA)
HKG - SEA (Air Canada)

In this example two different airlines BUT same departure city. So now the UA ticket is definitely not nested as its the same city pairs.

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3)
YVR - HKG (UA) TICKET but AC flights
HKG - NRT (CX) Credit to AA
NRT - SEA (UA)
SEA - NRT (UA)

NRT - HKG (CX) Credit to AA
HKG - YVR (UA) TICKET but AC flights

What is this? You actually never go to any of the same airports. And the connection is done with different alliance.

Please help as I am thinking about doing a MEGA run and don't want to get into trouble....(nor do I want to call the airline)