Narn I Chîn Húrin 1: Túrins Fostering

[Aiwendil]

I still lean toward leaving out the parts of the lay that would be used merely for 'expansion' of finalized portions of the Narn. I agree with Aran:

Even when it does match and provides more detail, I hesitate in using it, because Tolkien seems to have thought most of the Narn to be finalized.

If Tolkien omitted from the Narn a detail found in the alliterative Lay, I think there's at least a reasonable case to be made that he did so because that detail had been rejected. In contrast to the more common situation where we have an older 'full version' and a briefer, more compressed later version, here we have a late full version. So I think the usual argument that details found in the older text were not rejected but merely suppressed holds less weight.