It seems that the surviving copy is not complete; both commentaries refer to portions of Berrad Airechta which we cannot identify, and the introduction (Atait dano rūidlesa tuaithe a Féniu, "There are, moreover, transactions of the people of a kingdom which are totally immune from claim in Irish law") implies there was some text preceding it.
[3]: 279, 281 According to Stacey, Berrad Airechta is "unquestionably a composite text" with multiple linguistic layers (the latest of which corresponds to 700 CE).
[4]: 31 Stacey argues the text was reworked from multiple sources to form a tract with a structure that mirrored the usual procedural schedule of a contract case (using etymological digressions to smooth the transitions between different material).
[4]: 31 Michael A. O'Brien suggested Berrad Airechta was a kind of handbook for working judges.
[4]: 53 The Old Irish word berrad in the title is translated literally as "shearing" or "shaving" by Thurneysen and Stacey.