Note that the conclusion of 2+ authors is not based only on the premise of naturalism (ie prophecy is always written after the fact). If this were so, it would be circular reasoning (prophecy is always written after the fact > Cyrus and Babylon part looks like a prophecy > so per premise, it was recorded after it happened). There are in fact many reasons to give for splitting the book into two or more authors
Zech. 13:8 prophesied that two-thirds of the Jews would be killed during the "great tribulation", specifically occurring at the end of 62 weeks of the last 70-weeks leading to the messiah (490 years, beginning in 1506BCE). Two-thirds would die and one third would be restored to their homeland, making the end of the gentile times. This must occur within a 7-year period from 1940-1947 per the Bible. It happened. How do you explain a prophecy by Zechariah at least 2400 years earlier being fulfilled?
Oh, I know what you will say. Anybody can make any prophecy work. It's just a coincidence! Thus I find it interesting that the Cyrus prophecy would have been taken seriously and considered impressive being dismissed as "circular" when modern prophecies are fulfilled though they were written thousands of years earlier.
Another incredible fulfillment is that of the four beasts of Daniel where four major world powers existing at the same time during the end-times show one single clear-cut military superpower. The Lion in the prophecy depicted with wings at first, but those wings being clipped and the world power becoming less like a beast and more human, represents Japan when it was an aggressive military power. But after the A-bomb attack on two civilian cities, Japan totally did a reverse and became anti-nuclear. That fits that prophecy. The Leopard with four heads and four wings and "power indeed" was thus the only world power with absolute military dominance. And that is precisely the case today. The USSR has faded off the scene as a great military threat and power in the world.
200 years doesn't compare to 2000 years. Knowing the correct fulfillment of prophecies in our modern times makes a big difference in understanding the Bible truly is a book of impressive inspiration.
Here's even one for Jehovah's witnesses! You know that prophecy about the vineyard workers? Where the 3rd through the 11th hour workers don't know in advance what they will get paid? That's about the witnesses. But we can extract chronology from this parable since a half-hour is 3.5 years, an hour is 7 years. Thus the 11 hours of work are the 77 years from 1914 to 1991. The messiah arrives in the "last hour" which is the 12th hour (i.e. 1991-1998). Even so, there is a distinction for the workers beginning with the third-hour workers which distinguish them from the 1st-hour workers. That is, the first-hour workers were contracted for a specific amount, the day's wage of a "penny". The penny represents the heavenly calling. So those first in the organization were all of the anointed and understood they were going to heaven. But then, some of the later ones coming in truly did not feel they were of the heavenly class. This became so apparent that in 1935 a secondary "eartly class" within the organization was officially recognized. Thus the organization was made up of two classes now, the heavenly class and the early class. But that is precisely what the parable refers to. You see the appearance of the 3rd-hour workers would be present 21 years after 1914. 21 plus 1914 is 1935. Now how did the Bible know that. That prophecy came from the time of Christ, now close to 2000 years ago as well.
And there are many more, so.... That old excuse about claiming the prophecies were written after the fact, that things could not be predicted is an incompetent claim made by persons who are inexperienced and amateur Biblicalists. On the other hand, it's amazing to see prophesies fulfilled in modern times and so precisely when you look at those things that have to happen in a specific year to fulfill certain prophecies or pattern.
Just one more! For instance, the Jews were prophesied to return to their homeland after this "great tribulation" (the Holocaust). Naturally, this would occur as a major jubilee event for them. Well guess what? 1947 falls on the 70th week jubilee for the Jews since that week began at the time of the Exodus, where the Exodus is the 1st jubilee. The return of the Jews in 455BCE from Babylon was the first jubilee of the third day of this 3430-year long week. So in other words, if you actually bother knowing and understanding the scriptures, there are lots of things that are implied involving chronology. Once that 3430-year long week (7 days of 70 weeks = 7 x 490 = 3430) was FIXED by the 70th week ending in 36CE based upon the 70th week of 7 years occurring from 29-36CE, then you can project the entire 3430-year long week and determine when the 70th jubilee period occurs. That is, for those not following, every 490 years is 10 x 49. Jubilees occur after every 49 years and is a sabbath year. But it is also the 1st year of the next 49 years. So every 490 years has ten jubilees (except the very first, of course). So if you have seven days of 70 weeks, a 70th jubilee period of 49 years will occur during the last 49 years. That would be something special for the Jews to celebrate their 70th jubilee week, right? If ever there was a time for them to be restored to their homeland to celebrate this major jubilee. Well, if the third day ends in 36CE, then four more days would end in 1996, since 4 x 490 = 1960, and 1960 +36 + 1996. So the last 49 years, the 70th jubilee week would begin 49 years earlier, which is 1947. 1947, of course, is the year of the Partition Agreement giving possession of Israel back to the Jews. It also marks, of course, the "end of the gentile times." So what this another coincidence? Is "circular reasoning" involved? No.
So those who do not want to believe the Bible is inspired or true, come up with imaginary contradictions and challenges, some of which can't be proven, like claiming what was written after the fact, etc. But make sure they stay uninformed about any prophecies during our day so that they think the Bible's prophecies are either fabricated or don't work. Fine for them. But for those to take a step further to actually look at the fulfillments or have been blessed with holy spirit to understand with "insight" many of the hidden secrets in the Bible, we know the prophecies work and so are thus quite impressed, indeed, that the Bible is inspired, absolutely; and so for this group, the faith in God and the Bible is reassured and confirmed. But you can't see the light if your eyes are tightly shut and you refuse to look. So the non-believers want to have their cake and eat it too. They don't bother with the details of the Bible that might be impressive as far as prophecy, and for others who are impressed with some of the older prophersies, they try and challenge that with unfounded excuses they've made for themselves. Isaiah's prophecy was indeed written 200 years before Cyrus conquered Babylon and they can't prove otherwise, but it's hard to disprove absolutely as well. Dismissing what they can of old prophecies based upon "circular reasoning" theory, and refusing to understand or look at the more impressive modern prophecies that clearly were written 2000 years or more in advance allows them to dismiss the Bible in their own minds and continuing sleeping. Well... it's not the reality. Especially not now that we have all the chronology prophecies all worked out and coordinated, even the modern ones.
BOTTOM LINE? Indeed, prophecies are impressive. Seeing into the future is impressive. And the Bible does that quite well and quite specifically, both with relative chronology as well as absolute dating. Unfortunately, the faith-building that can be derived from chronology and prophecy are often the very things ignored by the non-believers and even many believers. But for those who actually want to get the true picture of how effective the Bible is about fulfillment of prophecy, the information is out there. They need only search for it. A small price to pay in lieu of being deceived by Satan into thinking the Bible is just another book and has no ability to tell the future. No so.
JC