> In order for a vnode to exist *at all*, it must have been opened at some
> point.

That's very much not true.  A vnode can be created by any lookup,
which can happen in response to a bunch of system calls which will not
`open' it (such as stat(2)).  I believe there is also some vnode
caching stuff in NFS's `readdir plus' RPC.  And symlinks are never
actually `opened', per se.

If you mean in the more general sense of `possibly a long time, before
the current boot, possibly even by a different OS accessing the same
disk', then that's marginally true (modulo symlinks), but it's not
terribly interesting.