Supermicrosurgery refers to the anastomosis of sub-millimeter vessels. The size range of the vessels or nerve in supermicrosurgery is typically 0.3-0.8 mm. By that definition, distal replant surgery is a form of supermicrosurgery, although that term was not used when I was training.
A strong foundation in “basic” microsurgery, if you can call it that, is necessary before venturing to this more technically challenging type of microsurgery.