Yeah, it looks like if I factor in reserved space, adding a little extra, most failed copied happened when it was almost done -I'd guess between 90-95% finished.
I appreciate all the help.
I think I can mark this "solved", even on the additional extra questions that came up through the thread!
I'll post a new question on tinkering with root reserved and tailoring data storage to deal -or not- with this new knowledge.
Thank you all so much!!!