AT THIS POINT WE SAY THAT WE STOP STUDYING ROMAN LAW
Justinian's Corpus consisted of:
1) Institutes; textbooks drawn up for teaching purposes, mainly those of Gaius Institutions. > 533 AD
2)Digesta / Pandectea; literature of classical jurists (often not in it's original form). > 533 AD
3) Codex + Revised Codex; contained imperial legislation, the Revised Codex contained the laws promulgated since 530. > 534 AD
((4)) Novallae; interpolations of constitutions of Justinian and his successors. > Post 535 AD
The Corpus Iuris Civile = a legal source (even the Institutions because they are included in this). So everything that was not included in the Corpus was not a legal source.