The Book can be viewed as an index that can provide otherwise unknown, or difficult to find, information of an illegitimate birth, and thus the father.
Gellir edrych ar y Llyfr fel mynegai a all ddarparu gwybodaeth a fyddai fel arall yn anhysbys, neu'n anodd ei chanfod, am enedigaeth anghyfreithlon, ac felly'r tad.