I think Tolkien was simply "filling up the corners", adding details here and there to enrich the story. Given the almost infinite amount of detail involved, and the timespan involved in writing all the books, I wouldn't be surprised if he did forget a few things. I suppose he couldn't double check every detail, especially in work not intended for publication. I love hearing such details, though. Middle-earth wouldn't be quite the same without them.

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Although now long estranged, Man is not wholly lost nor wholly changed.
Dis-graced he may be, yet is not de-throned,
and keeps the rags of lordship once he owned:
Man, Sub-creator, the refracted Light
through whom is splintered from a single White
to many hues, and endlessly combined
in living shpes that move from mind to mind.
Though all the crannies of the world we filled
with Elves and Goblins, though we dared to build
Gods and their houses out of dark and light,
and sowed the seed of dragons--'twas our right
(used or misused). That right has not decayed:
We make still by the law in which we're made!