Nuluk-khizidûn & Nulukkizdîn
Both of these names are variations of Nuluk-khizdîn, the halls of the Petty-dwarves which later became Nargothrond. Nulukhizidûn is the early version. In the original manuscripts for The Silmarillion, it is scratched out, and the modified Nulukkhizdîn is written above. Nuluk-kizdîn, on the other hand, is simply a misspelling, as noted by Christopher Tolkien. Thus, both can be discarded.