In some manuscripts ‘Cneppyn Gwerthryniawn’ is given as one of several nicknames borne by Sypyn Cyfeiliog or Dafydd Bach ap Madog Wladaidd (q.v.), but as this Dafydd sang late in the 14th cent. he could not have been the original Cneppyn (see I.G.E., 1925 ed., clxvii et seq.).

In Cardiff MS. 38, a manuscript containing the ‘Pum Llyfr Kerddwriaeth’ (the Welsh medieval ‘ars poetica’) in the hand of William Cynwal (q.v.), and also in other 16th cent. copies of the same work, ‘Cnypyn Gwerthryniawn’ (or Gwerthryniawc) is mentioned as a grammarian, and his name precedes that of Dafydd Ddu Athro (q.v.). As the bardic grammar was based on Donatus, this fits in well with the statement by Gwilym Ddu, and suggests that the leading poet-teachers were in possession of a written grammar in Welsh as early as the 13th cent. if not earlier (see G. J. Williams, Gramadegau'r Penceirddiaid, xx-xxi).