in the Prologue.... around 1:21 to 1:27 you've got the crossing the Prophecy Of The North / The Helcaraxë On Foot theme echoing (Release LIII)
https://soundcloud.com/search?q=crossing%20the%20helcaraxe%20on%20foot
particularly 0:28 to 0:31 of that which existed in my head since the 90's and is the oldest part of the whole Silmarillion musical corpus apart from the Eärendillinwë main structure (Release I and XVIII both)
https://soundcloud.com/doug-stoothoff/earendil-piano-alternate-phrases
so your surmise is correct. cheers
see also echoes of Howard Shore during the Two Towers movie: compare here from 4:04 to 4:11 is the seed of a phrase i created throughout the Silmarillion Stuff and gave to the earlier couple (Beren and Luthien)
the beginning of The Quest of the Jewel (LXIV) has it for a few seconds
https://soundcloud.com/search?q=the%20quest%20of%20the%20jewel