HTBWC:
I used to figure Jeremiah might have some core preserved in his book
due to the fact thjat the book is attributed to Baruch who was a
historical figure. But sadly Jeremiah's words are 75% deuteronomist
theology which places it very late. The rest is a mass of oracles
mattching greek seers or historical narritives from Kings.
A core of the work is probably legitimate (at least to the period whether or not actually written by 'Jeremiah'). The Septuagint version suggests the version we now have is in a completely different order to the original, with the oracles against other nations that are now toward the end of the book originally placed between the first and second halves of what is now chapter 25.
Sadly
Ezekiel must be vomited out also. ... The fact is the prophecy on chapter 38-39 point to a time when
Israel is attacked by Selucids when Israel is under peace.
Ezekiel was definitely edited after the original writing (for example, the '390 days' was introduced later, and the Septuagint version implies that it originally referred to a 190 year period, which may correspond to the period from the fall of Israel until the exile referenced in Jeremiah 52:30). However, a core of the work probably was written during the exilic period, as it would otherwise more likely refer to the role Persia would play if it were composed after the Neo-Babylonian period - instead it only relegates Persia to one of the minor nations assisting the hypothetical 'Gog'.