[1] These non-identical lists were constructed on the premise that many of the leading Welsh families of their time could trace their descent to the "five royal tribes of Wales" or the "fifteen noble tribes of Gwynedd".
In the surviving manuscripts, the first occurrence of the "fifteen tribes of Gwynedd" is probably in parts written by Gutun Owain in National Library of Wales NLW Peniarth MS 131.
[2] The Welsh headings which stand above the pedigrees of Eunydd of Dyffryn Clwyd and Hwfa ap Cynddelw on p. 85 and the tribe of Gollwyn ap Tangno on p. 90 all read something like "one of the 15 tribes (llwyth)".
A related list is found in British Library Add MS 14919, f.
The basic idea of five regal and fifteen common (i.e. noble) tribes was later used by the antiquarian and genealogist Philip Yorke as a model for his Royal Tribes of Wales (1799).