Even if he were flesh and blood and not a physical facsimile of Sparda, why would it only be possible for his body to be turned into shards? When Dante defeats demons, their souls are actually fluid, physical things: you can see them floating towards Dante. So what if the DMC4 library meant that Vergil's soul was hard, and it somehow shattered? Then those shards were used to create Bianco Angelos. That would explain why the file literally says those demons are made of fragments of Nero Angelo.
Seems like Capcom has yet another thing (besides Nero and his arm, I mean) to explain. This is going to be a huge undertaking for Capcom - let's hope they don't F it up as usual. Let's hope they actually get some decent writers and manage to keep them.
What I'm trying to say is, there's no evidence for anything. You say that it's obvious that the DMC4 library meant that those demons were made out of fragments of Nero Angelo's armor, but really, you're just guessing. We don't even know if Nero Angelo's armor still existed after DMC1. For all we know, Mundus utterly destroyed it. So how can you be so sure that those demons were made out of Nero Angelo's armor?
We don't know anything right now. The only thing we've got to go on is the DMC4 library file on Bianco Angelos being made out of fragments of Nero Angelo. I'm not willing to make a blatant guess like you are - the only logical thing to do right now is to stick with the DMC4 library explanation, and we'll see what Capcom really meant *later*. We'll see if they'll explain it in DMC4 SE.