Sui generis
A similar case that led to the use of the label "sui generis" is the relationship of New Caledonia relative to France, because the legal status of New Caledonia can aptly be said to lie somewhere between a French overseas collectivity and a sovereign nation. Although other examples of such status for other dependent or disputed territories may exist, this arrangement is unique within the French realm.
Status in Roman legal system
"Status familiae" is the legal status of an individual in the family. The pater familias had the authority in the family (patria potestas), and everyone was subjected to him based on adgnatio (kinship only from father's side). This had an impact in private law. There is a distinction between alieni iuris (persons under patria potestas) and sui iuris (persons autonomous of patria potestas, who could only be the pater familias himself).
Filius familias had ius suffragii and ius honorum, but in the area of private law he was restricted because of patria potestas.