For the convenience of current and future scholars and poets, here are the key source texts of the 1915-1924 Taliesin controversy in chronological order:
1. John Gwenogvryn Evans, Facsimile & text of the Book of Taliesin, 1916.
2. John Gwenogvryn Evans, Poems from the Book of Taliesin, 1916. Complete translations by Evans from the original manuscript, completed over seven years. Evans had been a speaker of Welsh in Carmarthenshire until age 19, when he learned English, but thereafter lived in England (he later retired to Wales).
Note that, “Though thus dated [1910 and 1915 respectively], the volumes [above] were not issued until 1916.” — Y Cymmrodor, 1918.
3. The Athenaeum, 1916, issues 4601-4612. Review by Quiggin of Evans’s book editions of Taliesin. A substantial section is given in Y Cymmrodor, 1924.
4. John Morris-Jones, Y Cymmrodor 1918, Vol 24. A substantial attack on Evans for his edition of Taliesin, and with a very strong Welsh nationalist flavour to it. The review was assisted by Ifor Williams. See Evans’s 1924 rebuttal.
5. Gilbert Waterhouse, The Year Book of Modern Languages, 1920. Annual review of the recent Celtic literature, and which addresses the dating of the life of Taliesin. “John Morris-Jones undertook to review Dr Gwenogvryn Evans’ two volumes on Taliesin [but he supports] his linguistic arguments with rather slender palaeographical evidence”. (At Google Books in Preview).
6. John Gwenogvryn Evans, Y Cymmrodor 1924, Vol. 34. Evans’s book-length reply to his 1918 critic.
7. Obituary of John Gwenogvryn Evans, J. Vendryes in Revue celtique 47, 1930.
8. At 2016 Angela Grant has recently completed a thesis at Jesus College, Oxford: “The View from the Fountain Head: the Rise and Fall of John Gwenogvryn Evans”.