Alistair, thanks for confirming my comments on this.
Jon, what exactly do you need from Chris that hasn't been answered? It has been explained by Martins wood buyer, as well as a number of Martin enthusiasts, Martin uses Genuine Mahogany for the necks, but reserves the right to substitute other woods like Spanish Cedar at their discretion. BTW, Spanish Cedar is what was used on all those vintage guitars selling for hundreds of thousands of dollars, so good stuff.