Glorfindel was one of the Twelve Captains of Gondolin who was killed in single combat with a Balrog as Tuor's party were attemting to flee the sack of the city. But, who should we meet six thousand years later, galloping along the roads of Eriador, looking for a handful of Hobbits, none other than the long deceased Glorfindel!

Tolkien realized he has erred and admitted that the use of the name Glorfindel in the LotR "was not given adequate reconsideration [before it went to print]." But rather than admit the error Tolkien came up with this business about Glorfindel being released from Mandos and returning to Middle-earth sometime during the Second (or maybe Third) Age.

I don't doubt that the Eldar could be released from Mandos (we know that Finrod Felagund was), but to suggest they could return to Middle-earth strains all credibility. After all, why only Glorfindel? If the Valar really wanted to help Gil-galad why not send back 10,000 knights of Gondolin?

Even CJRT found the idea hard to swallow, and suggested his father could have got round the problem by simply changing the name of Glorfindel of Gondolin (i.e. so it wasn't Glorfindel who died fighting the Balrog, but one of the other Captains).

But still, even the best of us mistakes, and some of us even try to cover them up!