Some prophecies were accurate because, quite simply, they were written after the event it purports to have foreseen. The Book of Daniel is a good example of this. It pretends to have been written during the time of the exile, that is around the sixth century BCE. Today, it is has been shown that Daniel was actually written around the second century BCE.
The prophet Isaiah, for instance, foretold the drying up of all the waters of the Egypt, and the destruction of all land used for plantation due to this drying up of the River Nile.
And the waters of the Nile will be dried up, and the river will be parched and dry; and its canal will become foul, and the branches of Egypt's Nile will diminish and dry up, reeds and rushes will rot away. There will be bare places by the Nile, on the brink of the Nile, and all that is sown by the Nile will dry up, be driven away, and be no more.
This part of Isaiah, widely accepted by scholars to be written around the eighth century BC, is about 2750 years old. And in all this period of two and three quarters millennia, this prophecy has yet to be fulfilled! Moreover it is clear from the context that Isaiah prophecy was meant for the Egypt of his time. For it was with that Egypt that Isaiah and his people had a grievance against, and the prophecy was a warning to them. Obviously this is a clear example of an unfulfilled prophecy.
In a similar vein, Isaiah predicted the complete and utter destruction of Damascus.
As noted above, it is now almost three millennia since that prophecy and Damascus remains a vibrant city to this day. While Damascus had been overran many times in its past, it is still around. Thus the prophecy that says Damascus will cease to be a city forever is obviously false.Isaiah 17:1-2
An oracle concerning Damascus. See, Damascus will cease to be a city, and will become a heap of ruins. Her towns will be deserted forever...