Leolaia , as usual you've been very thorough. Your research confirms for me that there was never a simple and single understanding of the topography of the world in ancient times, but particularly those that influenced the Bible writers. That's mainly why I objected to use of "corners" in association with flatness. Your explanation of "four corners" to reflect the cardinal points is much more apropos than my "corners of the room" analogy.
I was reminded of a depiction of the Hindu universe island sitting on 4 elephants, or the references in Job about the "pillars" of the earth (even though a number is not specified) or the Chinese folk religion that specifies four mountains as the pillars of the world or the four pillars that helped Shu the Egyptian god of air hold up the sky, etc. That number pops up all over the place in reference to ancient concepts of the world.

I'm not clear about the Hebrew concept of the world regarding the order of the "world layers". While it would appear that a circular earth surrounded by a circular ocean sat on some foundations (pillars), my reading of the texts that refer to both (the earth and watery deep) do not really indicate which sits atop of which. Here's one depiction where the earth sits on top of the oceans but the pillars are holding it up while embedded in "watery deep". It's different from other depictions where the "island" earth surrounded by the oceans sits atop something else (or not).

While it's very informative and fascinating in themselves, there's no point making sense of what the ancients believed in comparison to each other since their creations are essentially self-contained. However, it's easy to see how one influenced the other or several others.
Even though I find that humanity in those days would have had a problem conceiving how people on the other side of a spherical world might not fall off, and even though it's unlikely that they actually thought of a spherical world (sans the elephants, snakes and turtles, air gods and what-have-you), I can't totally rule out that they didn't have some concept of the curvature of the earth, although a very incomplete one.
Since ideas in science don't just spring up out of nowhere, it's possible that by the time the Greeks (3rd Century B.C.) hit on the spherical nature of Earth, some other prior cultures had the foundations for it. One clue is the compensations the Hindus made for the latitudes while using sun dials. That's a very important clue and indicator of curvature in the landscape. There's evidence that the Greeks (at or before the Hellenistic period) "borrowed" from the Hindus, which eventually led them to the "two-sphere" cosmic model.
Even though we strayed off topic, I believe that this conversation should establish sufficiently for Recovery that there are inconsistencies in the Bible and that what they believed is a far cry from what we know in the present, as the WTBTS would have people believe. My particular attitude is that if we can question, doubt, debate and discuss issues like this, it means we not only have the freedom to do so, but we have the right to dissent and not be forced to make conclusions where none are forthcoming. That's the real distinction of truth.