OK this is interesting -The band was that of the old RVC and so nothing to do with army cadets in the normal sense. The cadet corps band merged with the former Volunteers band in 1913 which may suggest that the cadet corps ceased to exist as an independent entity hence no entry in the WW1 Army Lists.
Melingriffith tin works does not have any connection to Bute that I can find so I can't make the wyvern link to Melingriffith or any pre-WW1 cadet corps.
I remain of the opinion that the cap badge sold yesterday is nothing to do with the attribution at all. It's huge leap of faith to connect the wyvern to a non affiliated welsh cadet unit.
At the other end of the interwar period it is not listed as a cadet corps in 1939's list of all cadet units
https://digital.nls.uk/dcn23/1044/1430/104414300.23.pdf