From the Appendix A:

Fengel. He was the third son and fourth child of Folcwine. He is not remembered with praise. He was greedy of food and of gold, and at strife with his marshals, and with his children. Thengel, his third child and only son, left Rohan when he came to manhood and lived long in Gondor, and won honour in the service of Turgon.

2905-80 Thengel. He took no wife until late, but in 2943 he wedded Morwen of Lossarnach in Gondor, though she was seventeen years the younger. She bore him three children in Gondor, of whom Théoden, the second, was his only son. When Fengel died the Rohirrim recalled him, and he returned unwillingly. But he proved a good and wise king; though the speech of Gondor was used in his house, and not all men thought that good. Morwen bore him two more daughters in Rohan; and the last, Théodwyn, was the fairest, though she came late (2963), the child of his age. Her brother loved her dearly. It was soon after Thengel's return that Saruman declared himself Lord of Isengard and began to give trouble to Rohan, encroaching on its borders and supporting its enemies.

Mithril - Book: Return of the King...chapter Minas Tirith..."but the helms gleamed with a flame of silver, for they were indeed wrought of mithril, heirlooms from the glory of old days." This is when Pippin and Gandalf go to Gondor/Minas Tirith. So I felt mithril was, though rare, a part of Gondor and it's trappings.

2937 - The story of the Horn from LOTR – JRRT
Oath paraphrased from one on dragonbear.com   With many thanks for much help – Linaewen, you rock!

2953 Chapter 13 - - Please note - much of this was postulated based upon ROTK – Chapter Five and also thoughts from – 'The Men Who Would Be Steward' by Michael Martinez.

2988
AUTHOR'S NOTES: From a deep-seated belief that I am unable to change or help a person who has chosen to die. I can do everything in my power to try to help them, from prayer to forcing them to seek counsel, to personally attacking them, to whining, to tears, to separation, to loving them. I can do everything – but they must chose to live. Someone near and dear to me, my sweet and precious husband, chose not to live. I have lived through the description of the tears and the odd questions that surface in the midst of despair and heartache and death.

I ran from writing this part of 2988 because of this. But standing upon the rocks of New Zealand, with my dear friends Indis and Elentari above a seashore that could have been Dol Amroth, Denethor cried out to me – write of her death, tell of my sorrow, speak my pain. And so, after three days of tears in the midst of the beauty of that island, I wrote of Finduilas death. May Eru be praised that I was able to write it. Amdir's death just happened. One morning, I woke up and knew he had to die. Sometimes, I hate my muse.

The 'Dol Amroth' room that Boromir created is based upon a room in a mansion that I was blessed to visit this summer. I knew it was Finduilas' room as soon as I saw it.

NOTES: *My apologies for the language used… see Tolkien's notes below… regarding the familiar form I use for Denethor, Finduilas and their children…. Forgive me if I am wrong, but it brings warmth to my heart to hear them speak thus.
Appendix F - I The languages and Peoples of the Third Age
So that at the time of the War of the Ring the Elven-tongue was known to only a small part of the peoples of Gondor, and spoken daily by fewer. These dwelt mostly in Minas Tirith and the townlands adjacent, and in the land of the tributary princes of Dol Amroth.

(The Rohirrim) They still spoke their ancestral tongue …. But the lords of that people used the Common Speech freely, and spoke it nobly after the manner of their allies in Gondor; for in Gondor whence it came the Westron kept still a more gracious and antique style.

The Westron tongue made in the pronouns of the second person (and often also in those of the third) a distinction, independent of number, between 'familiar' and 'deferential' forms…. This was one of the things referred to when people of Gondor spoke of the strangeness of Hobbit-speech. Peregrin Took, for instance, in his first few days in Minas Tirith used the familiar forms to people of all ranks, including the Lord Denethor himself. This may have amused the aged Steward, but it must have astonished his servants. No doubt this free use of the familiar forms helped to spread the popular rumour that Peregrin was a person of very high rank in his own country

For TA 2997 - as for mumakil - I can find no entries prior to the time of Denethor about these great beasts... so I am taking a little leeway (not usual for me) and suggesting that they might have just been bred within this age. Therefore, they are new to the men of Gondor. Just my own thoughts on this.