Though the information about Glorfindel was revised several times, both before and after Tolkien's death, it appears the professor did intend for the two Glorfindels to be one and the same. He was known to re-use names, often with the justification of the later incarnation perhaps having been named after the previous. Rúmil is one example of this. The Rúmil who encountered the Fellowship on the borders of Lórien was specifically written as NOT the same Rúmil who was the inventor of written letters. The two Glorfindels are less clear. At one point, Tolkien appeared to say he HAD intended for the two to be the same, and at another, he said he did NOT intend that.

But if they were the same elf, how is that possible? Did he not die in the First Age?

Once Tolkien decided that he did wish for the two Glorfindel's to be the same person, it led to more unanswered questions, most of which were not answered by Tolkien himself. While it is true that elves that are killed are reborn in Valinor (after a time in the Mandos' Halls to cleanse them of fault and impurity), whether he intended for any elves to be reborn to Middle Earth is less clear.

Which of course leads a person to speculate....if it was so rare for elves to be re-born in Middle Earth, why was Glorfindel one that was? Was he forced to, or was it a choice? After dying a horribly painful, violent death, it hardly seems as if he would choose to return....or would he?

He died in Gondolin protecting and saving the innocents; the females and elflings. One of those he saved was Eärendil, the grandson of Turgon, king of Gondolin. Eärendil was only approximately seven years old (depending on which source you believe, Tolkien contradicted himself many times about exactly when Gondolin fell, but it is certain that regardless of his exact age, Eärendil was very young, just an elfling) when Gondolin fell, but later married and fathered twins, Elros Tar-Minyatur and Lord Elrond of Rivendell. The same Lord Elrond that Glorfindel later ended up serving after his re-birth.

Which leads one to speculate....was he given a choice? Did Námo (the technically correct name for the Valar of the afterlife who is often called Mandos) give him a choice? Was he offered an eternity of peace and serenity in Valinor, or to return to Middle Earth? Of course, this is all in the realm of speculation, but I have found this to be a view shared by many others. This view suggests:

Glorfindel had been a warrior his entire life and knew little of a life away from that. When Morgoth's evil creatures attacked Gondolin, he had no thought of running, no thought of abandoning his king, his friends, his city. He took up a sword and began killing as many of the foul beasts as he could. Once the city was lost, and Turgon killed, he did what he knew his king would have wanted; he fled with the survivors, protecting them even unto his own death.

In Mandos' Halls, after a suitable time to cleanse his spirit and his mind of the horrible memory of his death, he was given a choice. He could live out the rest of his days in Valinor, his every need catered to, given a hero's welcome. Or he could return to Middle Earth, resume the life of a warrior, but with one irresistible advantage for a born warrior....he would get another chance. He had failed in his mission to protect his king in Gondolin....but he had saved the king's grandson. And was now given a chance to serve the king's great-grandson. To make amends for his failure in Gondolin. He chose to return, to serve Elrond....to protect him, and his new home of Rivendell, as he had failed to protect Gondolin.

Is this fact? No, nothing but supposition, and a way of explaining why he would have been re-born in Middle Earth instead of Valinor.