I wonder if the logging itself is different also, as I seem to recall timber cutters only cutting when the trees were dormant(sap down, they used to say), and I wonder if there is as much concern for that in the world today. And the old veneer was generally thicker. 1/28 in the late 60's, 1/42 to 1/64 is common now. I used to haunt a few veneer mills about here(always on the lookoout for fine stuff), and they were often known to brag that even there 1/64 wasn't a true thickness.
I really think some of the old sawn I have seen was closer to 1/12 or so.