Please check out the picture of a very early cruck frame located near my home in North Hampshire that has gable end oak cruck blades that are rip (see) sawn down through the heart to form a book matched pair set in the same cross frame. This is very easy to determine simply by looking at the mirror image of knots and other defects as they appear opposite directly one and other.
I am not aware of halved cruck blades being used along side each other i.e. on the same side of the timber-frame but that does not mean that this has never happened and it might well afford some benefits in terms of providing similar alignment arrangements for carrying side purlins. This could provide a very practical solution for a single bay frame.
Your comments about the St Lawrence seaway / UCV elm is interesting. I have noted that one of the 20+ year old English elms that I felled in my own garden nearly 10 years ago has annual growth ring widths of one half to three quarters of an inch. It appears that elm can achieve these remarkable growth rates during the early years of regrowth from suckers presumably because the main root system has remained intact and is still fully functional even after Dutch elm disease has killed off the main stem. What did you observe in the early growth rates of the UCV elm ?