I have no idea. Some say that 1st and 2nd Samuel used to be one book. I think that these are the kinds of minor edits that were spoken of by some of the ancients that later generations turned into "corruptions of the Word" and blew way out of proportion
and added their religious lies about for future generations. In one sense, there have been changes over the millenia, but in another sense the Word's never changed. This partially answers the riddle without my getting into other things. I've seen some scholars claim that Isaiah was originally two books and that the Mosaic Law was originally one book instead of five or six (some attribute Job to Moses).
We have everything that was said. We just don't have it necessarily in the same packaging as we'd of previously had it. The divisions of stuff may have been to aid Rabbinical schools in "rightly dividing the Word" while they were teaching. Stuff that got combined might have been combined to make it easier to preserve during times of intense persecution, or perhaps to relate the whole text to certain religious festivals.
Have you seen what Torah scrolls look like? They're monstrocities! Bigger than the ol' "family Bible" KJV that nobody takes to Church but leaves on the coffee table or on the book shelve. The chapter number and verse number designations are completely unreliable and are only a few hundred years old. Those were put together simply to be able to say where this or that was at, and not to be the beginning or ending of God's thoughts. Thanks for pointing out the level of design in the Bible. BTW: one thing you didn't cite in your stats is that the middle two words in the Bible are "the LORD"
The book still shows it's divine origins regardless of the nay-sayers.
If upon further research you discover that the two Psalms that got combined were combined fairly recently, perhaps it was a typographical error when people were still dealing in hand written copies or an oops when the really really tedious first printing presses came along and they just left the Psalm combination rather than mess with admiting they'd made a mistake. Somebody may have wanted a rounded off number of 150 Psalms rather than 151. Many teachers teach that the five books of Psalms correspond to the five books of the Torah, so maybe that simplified really bringing that out. Or maybe it was particularly meaningful to have those two Psalms in that way by some of the priests during the dark ages and the tradition stuck. If I ever wound up being able to have such an influence, I personally tend to stick Psalm 103 and Psalm 104 together as one Psalm in my private reading or if they ever have a baring on something I'm sharing. I've read 'em so often that it's just obvious to me that they're a little lop-sided without each other to paint the full picture.