There are 3 newspaper reports in the WNO which, I believe, reference your John James Hughes. These can be isolated by selecting the 1910-1919 decade & then specifying the Cambrian News via the drop down menu.
These selections should lead you to articles dated 24 December 1915; 7 December 1917 & 18 April 1919.
Of these the second may be particularly helpful as it refers to 'John James Hughes, Caledfryn' - which dovetails neatly with the same address recorded in respect of the 1962 burial for a John James Hughes in Llanfihangel y Creuddyn.
The first article also looks promising as it mentions him serving with the Cardiganshire Battery of the RFA. Promising because, the history in this link
https://ww1.wales/local-military-units/cardigan-battery-royal-field-artillery/ reveals that the battery embarked for France 'from 20 November 1915'.
Which date in turn further dovetails with the medals card (in Ancestry) for J J Hughes 730751 (formerly 1842 - perhaps his original service number?) which shows that his 'date of entry [to France]' was 21 November 1915.
Willyam