I don't see how this would invalidate the legitimacy of the documentation. The Hittites were large enough to be visible to contemporary historians and scriptures were used for information preserval. Even if our knowledge was only preserved through written documents, we'd have a good grasp of history 300 years ago, especially of major societies. People weren't primitive back then, they even had state archives with historical records which the Bible mentions in a few places for further reading.
That isn't to say that the Biblical texts can't reflect a memory passed on through oral tradition or knowledge from Mesopotamia and Egypt. But given that the geography of the Hittites of the Bible seems to line up more with the later "Neo-Hittite" Luwian-Arameans than Ḫattuša and that the Bible doesn't seem to be aware of the empire of Ḫattuša, the Biblical Hittites are probably not Ḫattuša.
Try 500 to 700 years. (Hittites collapsed around 1200 BC, the Old Testament was penned between the 700s and 500s BC.)
So some references from the Old Testament may correspond to people or places from many centuries earlier than the time when it was assembled, similarly to works like the Iliad and the Odyssey.