methods

[mwm1752]

When you add up the heat created in each of the four conductors, you see that although four conductors actually carry current, the heat produced is no greater than you would get from a maximum load on three conductors.
The count of CCCs to use for derating is not the same as the number of Cs Cing C.

Your statement is on target with theory to back it up. Comments as such put a great perspective on this subject. The same could be said about 2 wire circuits. The 2014 has commentary on non linear loads and there effects at the back cover.
When you add up the heat created in each of the 2 conductors, you see that although 2 conductors actually carry current, the heat produced is no greater than you would get from a maximum load on 1 conductors.