I am not so sure that you can discount the John CORDIAL on the Matchless. In 1841 he was, as we know, with his parents in Wales. Obviously, as he was born in Ireland, he would be familiar with sea travel. Aberystwyth, (44 miles away from Newtown),is mentioned thus by Wikipedia:
The port of Aberystwyth, although it is small and relatively inconsequential today, used to be an important Atlantic Ocean entryway. It was used to ship locally, to Ireland and even as a Transatlantic departure point. Commercially, the once important Cardiganshire lead mines shipped out of this locations also.
Seems possible that he went to sea, and crewed on the Matchless. Where were his parents by 1851? As he would have been 25 by then it would be surprising if he was still with them.
Judith