OK, so here is a prophesy that it doesn't matter when it was written, as long as it wasn't altered in our Bibles in the last 100 or so years, and I think you will agree that nobody has changed these verses in the last 100 years to make it look like prophecy fulfilled. There are too many copies of the Bible in too many languages for someone to have inserted these verses recently.
The prophesy is that God would scatter them into distant lands, then He would bring them back. Not only is this found in Isaiah, so we have a manuscript that has been proven to exist with this verse in it from before Jesus' time, but at least two other, different Old Testament prophets foretold the same thing.
The interesting thing about Isaiah is that is says "second time." There was a previous return, hundred of years before Jesus came, to the land of Israel. Then God said that in the future, He would scatter them again, and a second time bring them back. And how many times has the nation of Israel been regathered since they were scattered, I think around the destruction of the Jewish temple in 70 AD, but I haven't looked into it to know the exact year. ZERO TIMES, until the last 100 or so years.
There is evidence here, but I think some people really don't want to investigate it.
Isaiah 11:11
11 In that day the Lord will reach out his hand a second time to reclaim the surviving remnant of his people from Assyria, from Lower Egypt, from Upper Egypt, from Cush, from Elam, from Babylonia, from Hamath and from the islands of the Mediterranean.
12 He will raise a banner for the nations
and gather the exiles of Israel;
he will assemble the scattered people of Judah
from the four quarters of the earth.
Zechariah 10:10
Though I scatter them among the peoples,
yet in distant lands they will remember me.
They and their children will survive,
and they will return.
10 I will bring them back from Egypt
and gather them from Assyria.
I will bring them to Gilead and Lebanon,
and there will not be room enough for them.
Jeremaiah 23:3
3 “I myself will gather the remnant of my flock out of all the countries where I have driven them and will bring them back to their pasture, where they will be fruitful and increase in number.