Celeborn and his shaded past

[Ibrîniðilpathânezel]

I believe that it is important for one to consider Tolkien's final statement about Celeborn that appears in the letters, because it was made in December of 1972, less than a year before he died. He is answering questions about various names and Quenya vs. Sindarin, and says (letter 347):

Celeborn is a translation of the original name Teleporno; though said to be a kinsman of Elu Thingol he was so only far off, for he too came from Valinor.

Even amid all the revisions and alterations that were still ongoing at the time of his death, this statement, made late in his life, would to me indicate that this was very likely Tolkien's ultimate decision on the matter. We cannot know for certain, obviously, but I would consider this statement more "final," closer to what he envisioned as the most desirable form for his legendarium than statements made earlier. But that's just me.

As to Treebeard's allusion to Galadriel and Celeborn having more than one child, I would not dismiss it out of hand, since there are other characters in this mythology who had more than one child, but not all were actually named. Aragorn and Arwen come first to mind; we only know the name of their son and heir, not any of their daughters who are mentioned only in brief passing.