That’s the big question, isn’t it?
My best try at a theory to come up with a “how” I already posted above.
I just thought of another thing, though:
I’m not even sure it was ever mentioned in G1 that the Vahi was only one half of a mask.
Was there anything indicating that it wasn’t a complete mask in G1? If yes I would be most curious about where that information comes from.
The only thing that suggests that the Vahi in Gen 1 was only half a mask is it’s appearance. If the intention wasn’t to have it as just half a mask in 2003-2004, it certainly is now in Gen 2. The question is: how does this affect Gen 1? I’m not arguing that both generations are linked together, but you can’t deny that they have many similarities. Is the upper half of the Vahi one of those similarities? We may not know for sure.