Sonny wrote in
:

I had/have no written plans, only a visual idea of the finished
product. Then, I visualized-worked backwards, in my mental planning,
as to each task to be done, in order to accomplish the end product.
With each individual task, I did measure, calculate, mark, scribe,
etc., but the general plans/schematics were in my head.

I'm always impressed by folk that can do that sort of thing
in their mind. I can't - I have to draw everything out on
a piece of paper, front, side, and top views, with dimensions.

1) The table top boards: Rough cut 2" thick, 11'10" long, about 19"
wide; air dried for 2 yrs before beginning work; After drying, they
were planed to 1 3/8" to 1 1/2" thick. There was some slight
variation in the planed thickness, along the length of each board,
because of 1) the large size of the boards and ....

Curious how you planed them. Do you have access to a monster
power planer, or a wide belt sander?

This separate assembly plan presented
another issue, with respect to expansion/contraction movement....
there would be open "cracks" (separation) along the mating surfaces.
This/these "opening" events will likely have to be corrected by,
periodically, manually closing the mating joints, from time to time.
I don't want to have to do this "manual closing".

Not sure I'm actually following this, but could you peg the
tenons from below, and keep the joints tight that way? Then
all the movement would be at the outer edge of the table.

John