This is the great urban legend of Elder Scrolls, a popular myth, and a shadowy retcon. Almost every major source incorrectly attaches the name 'Nedic' to the proto-Nords of Atmora. This is like Columbus calling the natives 'Indians.' The major sources never go into detail as to how these Nedic peoples arrived and achieved their unlikely spread over the entire continent in peaceful fashion to create unique, independent cultures and dramatic racial differences. Why? Because the sources simply attach "Nedic' to the Atmorans and have done with the issue! It falls apart in the face of examination. I found these clues by two searches on TIL.
Abadal-aPerrif's original tribe is unknown, but she grew up in Sard, anon Sardarvar Leed, where the Ayleids herded in men from across all the Niben: kothri, nede, al-gemha, men-of-'kreath (though these were later known to be imported from the North), keptu, men-of-ge (who were eventually destroyed when the Flower King Nilichi made great sacrifice to an insect god named [lost]), al-hared, men-of-ket, others; but this was Cyrod, the heart of the imperatum saliache, where men knew no freedom, even to keep family, or choice of name except in secret, and so to their alien masters all of these designations were irrelevant.
There are many kinds of men in old Cyrod, and only those of Falkreath are from the north. Atmora is not the home of mankind. We assume that it is, but the exceptions of the Kothringi and Redguards make it impossible to take it for granted.
http://www.imperial-library.info/mwbooks/frontier_conquest.shtml
Frontier Conquest and Accommodation dances around the issue, and when read without the false knowledge, it all falls into place.
3rd PGEThere is evidence that early beast men of one variety or another may have been the original inhabitants of High Rock, but the Aldmer coming from Summerset Isle were the first to settle and form permanent communities. The early Nedic people who arrived next were stumbling upon a highly sophisticated culture, and were quickly overwhelmed and absorbed. One of the earliest tales of Khosey describes a Nord raiding party attacking a group of what they presumed to be Aldmer, but who were, on closer inspection, a mongrel race between elf and human, the remnants of the earlier lost Nedic tribe. They were somewhat awkwardly called "Manmeri," but we know them today as Bretons.
So the xenophobic Aldmer formed a hybrid race and a matured culture with a parcel of violent, seal-clubbing immigrants? Not likely. They had been living with mankind for ages, which is why humans are present in their myths.
3rd PGEThe West is respected as Cyrodiil's iron hand: firm, unwavering, and ever-vigilant. The Cyro-Nords that settled it had relinquished the fertile Nibenay Valley long ago, determined to conquer the frontier. Their primitive ferocity was disinclined to magic or the need for industry, preferring bloody engagement and plunder instead. After they had captured the Nedic port-cities of the Strident coast, the Westerners embarked on a mastery of the sea.
The PGE is confused. Nedic people from the north (Nords) captured Nedic sea ports? That is either very bad wording or they captured them from the culturally and racially distinct humans who populated Nibenay, the source of Cyrodiil's strange traditions and cults, tattoos, rice cultivation, ancestor moths, the Alessian theocracy, the Marukhati and battlemage rulers.
An MK post"Two soldiers hobbled through long grass to get to the lagoon. They carried knives and blowguns and painted faces and a hemprope of varliance beads that they may or may not use. The tallest of the soldiers, who the junglemen called Pellani, carried a staff with bones hanging from it and wet feathers and more the bones were these: one from a black sugarcat which made him invisible to his enemies, four from the neck of a Snow Throat thane whose crimes still largely remain hidden, and of bird legs like clicking moon'd tinsel of no matching pair, and set highest on the staff, like an eye (for it was an eye), the white knuckle of an unborn child. His student beside him was a hoplite called Small Mori, who wore the bull tattoos of his tribe and a nose ring as in the fashion of the Revolution in the northern quarter of Ut Cyrod.
"The lagoon was surrounded by pretty rust-haired girls that all looked alike, grim dark on crush. I remember Gyetai, Pellani said. Small Mori's breed-father once shovel-skulled a Nail-Face for talking [censored] in the rice fields. Just let us take a skiff, one girl said.
"They've been testing this design back east, Small Mori said, and let's all get in. There can always be joy. They rowed in cursive across the water, sinking the bright varliance as they went, reminding the girl that her eyes were stars that didn't know how to swim. Pellani grabbed a ghost and slid his knife vertical down its belly. Inside was a map that no one heeded. No one needed, she said.
"And now the paddles, held straight in the rush that came, made great fins of water on either side of their skiff, and to call it repose was to taste one another. When she finally runs it's never really to get out. The facepaint had been stolen and made by eyelid hands.
"And just as they got to Delodiil the magic ran out. While Small Mori pilfered a stone from an ancient eyelid-wall, the girl hitched a ride back to camp on a crooked bonewagon whose sides were tagged by first generation feather-rebels. Pellani handed his friend something she left behind. And that's what Small Mori will always remember:
"Back at the lagoon and they were dancing and he said, what currency can I offer so you never run away, she had said: you can pay me in moans, brave bull, aad semblio elhno ky'n."
Lastly, I dare you to tell me with a straight face that these guys sound like Nords to you. Alessia was no Snow-Man.