I've always wondered...
Say you're playing LeBlanc (or any other champion that has delayed dmg abilities), you throw Sigil (or ethereal chains) at someone, if you upgrade the ability AND THEN proc the extra damage from Sigil, does the damage dealt reflect the skill point you added after the ability was cast? I've always been curious.
and level it up mid-air, it will increase the damage. So probably yes, not sure tho.