Maybe he wanted to first see the book actually being published, after this rather unbelievably long gestation period. I have now ordered the book too, there was no rush as I am waiting for the cheaper Princeton version. So I'm very much looking forward to some more of Harris's plates.
Thanks for the link to his website. Alan Harris is one of my favorites when it comes to book plates, but it's been quite some time since I checked his website. I may have mentioned that I have several of his originals. So I was rather surprised to see how many of them are still for sale. But then, unless you have space to exhibit them on a wall, it's of limited use if you're not an extreme collector. And if you are, you might not want to display them for fear of them fading.