I have always thought that there is going to be some variation due to the hand-built nature of the shoes, and the use of multiple lasts in the factory which may vary slightly. (I have to believe they've got more than one copy of the 65 last in size 10D.)
Of course this doesn't even account for different lasts having different shapes, and not fitting the same even if they are all a 13B.
Ideally, a size 13B on the 65 last would fit the same with every shoe. And perhaps some day that will be achieved. That's my dream!