Interesting. I believe this golden armored character from the 2013 here was the original Glauca design, in fact I think it was confirmed to be at a French screening of Kingsglaive that Nozue attended where they showed the audience some scenes that were cut which involved Ravus and Glauca, and he had the Golden armor design here.
Then when they started making the story changes around October 2013 when Kingsglaive started is probably when they also decided to change his design, and these were some of his concept redesigns.
And then his final.
Nihilarmy I'm pretty sure just refers to Niflheim army, since Niflheim has been romanized as "Nihilheim" on official artwork for XV before, so Nihiltower probably also just means some sort of Niflheim tower, could just be some random tower at a base or what have you.