The entire reason the book was dated after 37 B.C. was because the scholars presumed that prophesy is impossible, i.e. mentioning the end of the Maccabee reign would date the manuscript after 37 B.C., the rise of Herod the Great. Subsequent carbon-dating set the Qumran copy's date as far back as 186 B.C. (before Herod the Great and before the Maccabees as well).
They were wrong because they made a naturalistic presumption going into the investigation.
Now, the translators must look at the same passage as either a prophesy fulfilled or an accidentally accurate statement or metaphor made at least a century and a half earlier. The part about the "great horn" is in context with a full review or preview of Jewish history spanning two chapters, 89 and 90.
Actually, based on my brief reading, there was argument about this even before the carbon dating.
It does seem, though, that any inferences they made based on a very stretched reading of the manuscript were questionable to start with. Based on a quick reading of 89 and 90, and the history of the Jews in the Maccabean period, I don't see much relationship between the two.