I remember that someone, maybe Christorpher Tolkien, gives a quite persuasive explanation on, or maybe I should use rationalizes here, the discrepancies among The History of Middle Earth, The Silmarillion, The Lord of The Ring as well as other Tolkien's books.
It's said: these books are accounts of Arda by differenct people or races . LOTR is based on Hobbits' accounts. HOME is based on Eldars' accounts. It's quite normal that after such a long time, no such accounts is an explicit description of the history itself. some omited, some faded into oblivion, and some altered. So at last, there are so many different versions of history in different eyes although there exists only one history. For example, in LOTR, it's G who throw the ring into the mountain doom. In HOME, it's F.
History is always covered by a mist. We can never know its true face.