Sanji names most of his techs after the body part he hits, in the end they are all just kicks, but they are still qualified as different attacks. In the end almost all of Zoro's techs are 'variations' of sword techs and those again are 'variations' of combat techs. It all depends on how broad or small your perspective is, but in the end Zoro/Oda has classified Zoro's techs as being unique depending on the number of swords used. Using one sword is a different tech than using two swords. The only exception is his Phoenix Cannon.
You used "Nitoryuu Daishinkan" as an example. Daishinkan is used by holding a single katana with two hands, it's a one-sword style tech. Even if Zoro would use a similar tech somehow with two swords, it would highly likely be under a different name and it would be classified as a different tech as it's not the same no matter how much they resemble each other. If he would however use the same name, then Zoro/oda intentionally wants them to related to each other.