As christep wrote, class of service and other factors affect routing.
seasonal flight such as DFW-ANC needs some consideration.
first class availability, A class booking for DONEX fare within NorthAmerica etc.
Furtheromre, entry VISA requirements also affect your planning.
ex-NRT XONE3
For example,
nrt-del-hkg-jfk-sju-dfw-anc-dfw-sju-lax-lhr-mct-lhr-ist-lhr-sin-nrt
55,406 miles
ex-NRT XONE4
nrt-del-hkg-jfk-sju-dfw-anc-dfw-sju-lax-scl-ccs-scl-ccs-scl-lax-lhr-mct-lhr-sin
-nrt
75,672 miles