Biblical doublets and JEPD.

The OT probably began to be a written scripture in exilic times.  Over time it became - amongst other things - a saga of the Hebrew people from the begining of the world to the time of the second temple.  It was a vast undertaking, probably unprecedented in scale.

One problem was how to weave together slightly (or sometimes very!) different traditions and versions into a single story, and on the whole the editors and redactors did a good job, but there are still clear signs of the OT being 'cobbled' together.

The first and best known is gen 1 and gen 2, which are different accounts of creation, clumsily(?) linked by Gen 2:4.   Just as well known is the ambiguity between the number of animals on Noahs ark - was it 2 of each, or 2 of some and 7 of others?

The story of Abraham passing his wife off as his sister appears 3 times, gen 12:10, gen 20:1 and gen 26:6.

There are 3 different accounts of Saul's ascent to kingship, and Goliath is killed by David in 1 Sam 17 and by Elhanan in 2 Sam 21.

2 kings 19 and Isaiah 37 are word-for-word identical chapters!

There are loads other 'doublets' in the text, even if you ignore Chronicles, because that was a later rewrite of the material. 

More thorough analysts than me identified 4 'strands' (JED and P) which are intertwined in the OT we have today.  I can't think of a good reason to doubt that is essentially true.

You seem to understand that these are speculations. And the truth really depends on the O.T.s relationship with divinely inspired authorship. Without that, the sky is really the limit in terms of how many author's, and editing were involved.

We have a big problem at the beginning of Genesis, because the type of authorship required to record "In the beginning" from an eye-witness perspective would be humanly impossible.

So if you would stretch your mind a bit (not that you haven't), giving the creation account the benefit of the doubt (if but for a fleeting moment) as being a factual historical account, who would you credit to, or possibly credit it to in terms of human authorship?

Translation: I admit that these passages are complete fiction but I'm gonna believe them anyway, just like the rest of the book. I know it's all fiction but it pacifies my fears. It's much nicer to believe than reality.