Slitherine

I have noticed in some army lists that a unit in the main army list can be upgraded but that upgrade does not appear in the allies section, does this mean the upgrade cannot be made?

i.e. Koryo Korean KwangGun cavalry can be upgraded to SingiGun in the main list but it does not show in the allies section.

Yes, that is correct, the allied contingent only has the options available in that part of the list.