The Core of the Elder Wand and other new JKR explanations

[Carol]

No: HPFGUIDX 179727

Carol earlier:
> > 
> > Does anyone besides me find this information less than helpful,
even possibly annoying? It isn't in the books (we don't even know that
the wand *has* a core), and it seems to me that a number of people 
became the master of the Elder Wand by seizing it or killing the
previous master without necessarily being capable of facing death.
> 
> Annemehr:
> 
> Well, now, I read this differently: I believe what JKR meant was
that working with thestral tail hair *itself* could only be done well
by someone "capable of facint death."  I.e. it would apply to a 
wandmaker who might use thestral tail-hair, but not necessarily to 
the wand-owner.  (I'd say it would also apply to anyone using it in a>
potion as well.)
<snip>
 
Carol again:

Okay, that makes sense. At any rate, the wandmaker would certainly
have to have *seen* death (and, per JKR with regard to Harry's not
seeing Thestrals at the end of GoF) processed or understood the
witnessed death to be able even to see the Thestrals, much less obtain
a tail hair and place it in a wand. So if it's the wandmaker the
eldest Peverell brother) rather than the master of the wand who's
"capable of facing death," I guess a Thestral hair core makes sense,
and yet, the brother who created the wand wanted it to be undefeatable
(in the legend, he was trying to *defeat* death by making himself
unkillable, which he certainly failed to do).
 
> > Carol, who prefers to believe that the Elder Wand was coreless <snip>
 
> Annemehr:
> 
> Coreless, huh?  The possibility never occurred to me; in fact, I was 
> irritated that DH never said what the Elder core was.  I'm glad JKR 
> finally said, but I wish she'd have put it in the book.

Carol:

Aside from the fact that the wood is mentioned but the core I not
specified, even by Ollivander, I thought of it as coreless because in
the legend, it's fashioned directly from the branch of an Elder tree,
no core involved. I realize, of course, that "The Tale of the three
Brothers" and the manufacture of the Hallows by the three Peverell
brothers are two different things, one legend and the other the
half-forgotten history of the objects. As in RL, the farther back an
incident occurs, the harder it is to distinguish one from the other.

Carol, suspecting that JKR never thought about the question until it
was asked and came up with an answer after the fact