I might as well weigh in, too !
Ed,as you know, I read and wrote a review of your book - noting I disagreed with you on certain aspects.
On of the things I disagreed with was your analysis od the handwriting-which I believe is quite consistent with the sort of printing one finds on hand-lettered posters.
I also think - but am not well enough informed to be sure-that the "doodling" you mention in the letters is,perhaps,not doodling, but an indication the writer was accustomed to one of the Germanic scripts.
kidding... was that for EdLake?