The Dark Elves are not a united people like the Wood Elves of Dragoc or High Elves of Froturn, but rather live in clans. We make a distinction between lesser clans and the three major clans. The difference is that the lesser clans truly are groups of Dark Elves united by actual or perceived kinship and descent, while the three major clans are more accurately described as states rather than clans.
Clanless Dark Elves do exist in the sense that they do not belong to any of the lesser clans, but even those "clanless" Dark Elves are "citizens" of one of the three major clans.
The three major clans
|Dhaeraow Loomin||Gurtha Ndengin||Mori Templa Mellon|
All of the three major clans are successor states of the Kingdom of Marand and are completely independent of each other, making all three of them sovereign states on their own. They also have various lesser clans as their vassals.
One does not have to be blood-related to the ruling class of these three clans to be considered a full-fledged member of them - being a member of one of their vassal lesser clans also warrants being considered a full-fledged member of the major clan.
Various lesser clans exist too, but none of them are independent or sovereign - every single one of them swears allegiance to one of their three major clans, which comes with benefits and responsibilities alike: recognizing the suzerainty of one of the three major clans automatically makes all of the lesser clan's members citizens of the major clan, which comes with both responsibilities and privileges.
Generally, switching aligances between the major clans is not possible, unless the lesser clan chooses to migrate to the territory of the other major clan. For similar reasons, going independent is also considered unpractical at best, suicidal at worst.