I'd also like to add, that because Copy X and X do not share souls, the only thing that makes Copy X, "X" is his being addressed as so. He's not really X, but it's the identity he was given. Girouette was never addressed as Zero.
Now, Girouette DOES bear a striking resemblance to Zero, and there's a pretty heavy implication that Prairie has taken notice of it:
"Hahaha! Maybe Giro resembles someone you cared about. Everytime you talk about him, you look so happy. Don't worry, I won't hold it against you if you did like him. It's thanks to all of you that I'm finally able to fight for what's important."
So, if you want to theorize that he was built in memory of Zero, that's fine and dandy. I wouldn't say that makes him "Copy Zero", though, since he first of all does not have any combat abilities of his own and secondly does have an identity of his own.
They are anything but irrelevant:
Okay, to that STATEMENT, even if they are addressed later on in the discussion. I apologize for my poor choice of words, but what I meant was that Aile was asking about herself personally, and Giro's involvement, thus Prairie responds in that context. The order, as your own quote shows, applies to a larger scale than that. But Aile isn't asking about the order, she's asking about her own identity.
His compatibility with Model Z is an unintended side effect. Much like Ashe who can use Model A because she's related to Albert, Giro can use Model Z because he shares its DNA data.
As Zan already stated Giro was chosen by Albert, which we know because he is in the ciphers in ZXA.
Further, one's DNA resembling that of the Biometal would be completely irrelevant. For all Biometals, it is Albert's DNA, and none other, which affects compatibility. No official word has ever suggested that there are any further compatibility checks beyond that (or as Zan once said, the idea that any Chosen One cannot use any Biometal is complete fanon).