Ahar I have found a quote upon his final thoughts re Glorfindel in the HOME books "The Return of the Shadow"
"Also very noteable is 'Glorfindel tells of his ancestry in Gondolin.' Years later, long after the publication of The Lord of the Rings, my father gave a great deal of thought to the matter of Glorfindel, and at that time he wrote : [The use of Glorfindel] in The Lord of the Rings is one of the cases of somewhat random use of the names found in the older legends, now referred to as The Silmarillion, which escaped reconsideration in the final published form of The Lord of the Rings.' He came to the conclusion that Glorfindel of Gondolin, who fell to his death in combat with a Balrog after the sack of the city and Glorfindel of Rivendell were one and the same : he was released from Mandos and returned to Middle-earth in the Second Age"