This description of the Book of Jeremiah is from Easton's Bible Dictionary.
"Jeremiah, Book of: consists of twenty-three separate and independent sections, arranged in five books.
In Egypt, after an interval, Jeremiah is supposed to have added three sections, viz., Jeremiah 37:1 - 39:18, 40:1 - 43:13, and 44:1-30.
The principal Messianic prophecies are found in Jeremiah 23:1-8, 31:31-40, and 33:14-26.
Jeremiah's prophecies are noted for the frequent repetitions found in them of the same words and phrases and imagery. They cover the period of about 30 years. They are not recorded in the order of time. When and under what circumstances this book assumed its present form we know not.
The LXX. Version of this book is, in its arrangement and in other particulars, singularly at variance with the original. The LXX. omits Jeremiah 10:6-8, 27:19-22, 29:16-20, 33:14-26, 39:14-26, 52:2,3,15,28-30, etc. About 2,700 words in all of the original are omitted. These omissions, etc., are capricious and arbitrary, and render the version unreliable."