Since making the above posting, I've become convinced that the evidence in relation to John's will probably does indicate a death date of "about 1777."
The clerk's note after the will reads this way:
"At Albemarle August Court 1777 "This will was proved by the Oath of the Witnesses thereto & Ordered to be Recorded, and at a Court held for the Same County January 8th 1778 on the Motion of Thomas Walker & Nicholas Lewis Executors therein named who made Oath According to Law Certificate, was granted them for obtaining a probat in due form, whereupon they gave Bond with Security & Acknowledged the Same Accordingly."
Knowing that courts sit during prescribed time periods (called "terms") and that a term of court can last for several months (for example, the U.S. Supreme Court's "October 1999" term lasts until summer 2000), and given that the reference to "August Court 1777" sits on a separate line, I had believed that that line referred to the term of court, and that "January 8th 1778" referred to the date, later during the same term, when the executors first presented the will to the court.
However, I've since noticed that the clerk's note for the will that precedes John Michie's will in the same will book begins with the line "At Albemarle July Court 1777".So apparently a term of that court, during the late 1770s, lasted a month or less.Also, Bill Cotton, another participant in this forum, has pointed out to me (by private e-mail) that public notice of the presentation of the will was required before the will could be probated, and that, if John had died in early 1778, there would not have been enough time after his death to complete the required notice by January 8.
So, with a little egg on my face, I acknowledge that our great, great, great, etc., etc., grandfather John Michie died "about 1777."