http://americanart.si.edu/maloof/design/fig171.jpg

Maloof appears to pin the crest rail through the back legs of that
chair. I can understand why he'd pin the chair rail tenons as a
drawbored M&T is quite sturdy indeed. But when he pins the crest rail,
he's boring through end grain. I would think those pins would weaken,
not strengthen, then chair. Then it occured to me. Maloof's not
pinning the crest rail tenon. Despite the round ends, those aren't
pins he's using. They're wedges.

That's just a guess. Am I right?