...right. (Also, jade has something called a "Mohs hardness" between 6.5 and 7, which amuses me to no end.)

Nephry and Saphir also take their names from gemstones; "Nephrite" is type of jade, while Saphir means "sapphire" in both French and German. If you look at the pictures on the ground in Keterburg you can see gemstone illustrations, though I'm not sure why they choose to name the Keterburg residents after stones. Perhaps it has something to do with Keterburg's association with "crown."

"Jade" may have another meaning as well. As an adjective, "jaded" means "worn out or wearied, as by overwork or overuse." Jade could be described as somewhat jaded, at least in comparison to the other members of the party. As an experienced soldier who has seen a lot in his lifetime, Jade seems to lack the enthusiasm and blatant determination of his companions. He even teases them for it, at one point sarcastically remarking, "My, my. What passion, what fervor!" as the excited group prepares for battle.

Jade's last names seem to be pretty much random. The only connection I can make with "Balfour" is the fact that it's the name of company that makes class rings, which was the first thing I thought of when Jade's identity was revealed. "Curtiss" is likely derived from the name "Curtis," which in turn comes from the Old French word curteis, meaning "refined." Possibly an allusion to the wealthy and famous family Jade was adopted into. Curteis is also the name of a jewelry company (thanks, Google!).