[Galin]

Maybe to give Imrahil a singular nobility among those who arrived to aid Minas Tirith, and a fairness even bordering on Elvishness, whether or not Legolas was correct?

I agree it seems odd to think that Legolas might be wrong, but for example when Turin reached full manhood he was (The Children of Hurin): "in truth the son of Morwen Eledhwen to look upon: tall, dark-haired and pale-skinned, with grey eyes, and his face more beautiful than any other among mortal men, in the Elder Days. His speech and bearing were those of the ancient kingdom of Doriath, and even among the Elves he might be taken at first meeting for one from the great houses of the Noldor."

Granted it says "at first meeting" here, but on the other hand we don't know what the eventual give away might be with Turin, who never claimed to be an Elf. When Tuor first enters Gondolin his eyes give away his kin, but earlier in the Narn Turin is described as bright-eyed as well, and I note he is compared to the Noldor here, whose eyes (at least early in their Exile anyway) were so notable that the Sindar called them Lechind "Flame-eyed" (Quendi And Eldar, War of the Jools).

Also Morwen was dark-haired and tall (The Children of Hurin) "and for the light of her glance and the beauty of her face men called her Eledhwen, the elven-fair..."

Legolas appears to have just met Imrahil when he notes the story ("at first meeting"), and even Imrahil stamps that this is the lore of his land, and I don't think (if I recall correctly), that Tolkien ever refers to this matter outside of the context of a legend, suggesting variant traditions concerning who the Elf maid was, if "improbably" Nimrodel herself.

Another thing is that after Mithrellas (of the Silvan race) bore a son and daughter, at some point she "slipped away by night and he saw her no more"... seems a bit odd for a mother to do this, and we are given no reason for the disappearance. But this does, somewhat conveniently in a way, take early care of the living proof of Elvish blood in the line, noting too that Mithrellas would not die as a mortal.

Sounds a bit like a good way to explain that the (Unfinished Tales): "... house and kin of the Lord of Dol Amroth was noble by blood as they were fair in face and mind."

So again, while I agree it's hard to think Legolas could be wrong about this, I'm not sure I should be certain he was right.

Or something else!

Edit: by the way, Happy Birthday Nerwen (I just noticed)