The author who rewrote The Book of Enoch made as (few) and (minimal) changes as he could. He was looking for the original text. Yet, there were other sections of the scroll of Enoch that were missing, resulting in certain verses being lost. There were literally fragments of Enoch's document that were lost or destroyed. As a result, the author felt well qualified to fill in the gaps in Enoch, having already authored the entire book of Nathan the prophet and the book of Gad the seer. Hence, instead of meddling with the sections of Enoch that we do have, the author filled in the blanks with trust.