In the imprecise prophecies department, consider Isaiah 7:8b. According to the narrative in 2 Kings and 2 Chronicles as well as extra-biblical sources, the conflict between Rezin, Pekah, and Ahaz occurred around 735 BCE. Damascus fell to Assyria just two years later, and within 13 years the whole of Aram and Israel had been conquered and scattered. Why, then, did Isaiah mention 65 years? Sure, we can say that at the 65 year point these nations were shattered, but what purpose could Isaiah have in extending the defeat so long when trying to encourage Ahaz? Either way, Ahaz did not survive to see the fall of Israel.
Verse 16, however, seems to get the time frame right: A child would reach the “age of accountability” at about 13 years old, which is when Israel fell.
And in a note related only by proximity in the text: Study notes in both the JSB and the HarCol point out that 7:20 describes shaving the head and the pubic hair.