Roxas is Sora's body and soul. Roxas is 2/3 of Sora. Aside from Ventus' crippled heart changing his form into that of Ventus and having said heart for most of his existence (Not going to get into whether Roxas exists or not), he's practically an alter-ego of Sora's. Roxas wants to be his own person, that's why he doesn't like being compared with Sora. But if he knew of Ventus he wouldn't want to be compared to him. Roxas isn't the same person as Ventus, but he is 2/3 of Sora. A nobody is a part of someone, Roxas is a part of one person. That Person is Sora.
On the surface every Keychain is either a KK or KK-D. These are dormant
memories as that is what Keychains are. In KH1 Sora recieved Keychains from other people, instead of just finding them. Ex: Three Wishes=Created when Aladdin met Genie. Once a person finds themself said Keychain awakens. (Going by what you said) Ven's transformed into Oathkeeper and Sora's tranformed Oblivion. The relevence of time is that it takes time for the dormant memory to awaken. Ven's originally turned into Wayward, but had to restart when Roxas summoned it then reawakened it into Oathkeeper. Basically what I'm trying to say is that my theory is Vanitas, MX, M.E. , Mickey, Aqua, and Terra's Keychains had already awakened by the time of BBS. If Vanitas had summoned his Keyblade right after being plucked out of Ven's heart and it was Void Gear than that would proof against it. But there are no first time summons that can disprove it. Seeing as each first time summon was using the same Keyblade. Also note that Mickey's Keychain:
Star Seeker is given to Sora, yet it's supposed to be only Mic's Keychain. Now if you want to assume that Mickey switched-out the Keychains so Sora could use it in KH2 and then switched-out the two (Keychain) for Coded, be my guest.
Let me get this straight, you used something that you don't know as a way to win the discussion? For the record, I'm saying all
STARTER KEYCHAINS look one of two ways on the surface. When they awaken they turn into something different. Keychains made from other memories will often be unique, but Oathkeeper, Oblivion, and Ultima Weapon are some of the few or many exceptions.
X-Blade or Death-Blade is not a Keyblade, nor is it a type of one (Not that it's relevent to the discussion).
In the report above ^ Xehanort reffers to the Keyblade being possibly a man-made counterparts of KH (Which kinda begs the question how if this is true). They represent memories, as if Keyblades really are supposed to mirror Kingdom Hearts then Memory may or may not be essential. But if we take Marluxia's words about Sora's heart being destroyed, it basically implies the Memory which these Keychains represent stabalize a Keyblade. Thus a Keyblade such as HO/KoPH is unstable, perhaps this could explain why it's able to unlock people's hearts in dangerous manner. However, the Death-Blade coexists with KH and has a Keychain of it's own, though perhaps that's one thing that seperates a Keyblade from the Death-Blade (It works without any draw-backs).
Seeing as Nobodies are so into artifical things (Replicas to name one) it wouldn't be hard to believe that Gears are artifical Keychains. However, that's more of shot in the dark, if not one with a few lit lamps to guide the way.
HO does/did not possess a Keychain
Not so sure a memory alone can choose, but who knows.