I have another question: Why is Kor not mentioned in the Silmarillion but talked about so much in the Unfinished Tales?
I think you might mean The Book of Lost Tales
, but basically, in the later Quenta Silmarillion Tirion upon T’na replaced T’na upon K’r. Notes in The History of Eriol or ’lfwine
include Heorrenda calling K’r (or Gw’r) T’n, and in context this is the Old English word t’n
from which modern English 'town' developed. T’na will be an Elvish word in any case, as noted (for example) in the later work Etymologies:
KOR- 'round' (...) K’r 'round hill upon which T’na (T’n) was built.' (...) TUN- (...) Noldorin tund, tunn hill, mound Q. T’n, T’na 'Elf-city in Valinor.'
In a version of Quenta Silmarillion written before The Lord of the Rings
was completed: upon the Hill of K’r was built T’na, the Hill-city, which the Gnomes in their later speech called T’n or Eled’n. In the later Quenta Silmarillion, as I say, Tirion upon T’na replaced T’na upon K’r.
Of course this is the shortened, perhaps less confusing explanation!
The name Melko was the name Tolkien was using for Melkor in the early drafts of his work. in these early drafts many names, places and entire plots became changed to what we now see in the Silmarillion
Also, it looks like Tolkien was going to pick up Melko
as an alternate form alongside Melkor
with respect to later conceptions, noting the glossary found in the 'Athrabeth section' of Morgoth's Ring.