Is an item only "official" or "traditional" if and when it is adopted by the UK military?

Some of the Irish that fought in the American revolution were rumored to have worn them. I will look for picture if I must. In addition the throng of Irish that arrived in the USA during the potato famine 1845 and 1852 worn them as well. Not to use Hollywood as a source of truth, but in gangs of Gangs of New Your you can see the caubeen worn by the Irish.

If it must go back to a military source, in 1641 Owen Roe O'Neill lead the Irish Confederate Forces against those of Charles I. In painting of him and the battle he is wearing what resembles a Caubeen. Image Here. Owen Roe (the red haired) O Neill (1590-1649), a nephew of the great Hugh O Neill, Earl of Tyrone, was a professional soldier who had served thirty years in the Spanish army. He returned to Ireland and, in 1642, joined the new movement styled the Confederate Catholics of Ireland. He defeated the Scots under Monro at Benburb in County Tyrone in 1646. The O'Neills were one of the 7 major Ulster clan of which the Owen clan spun off (County Tyrone is the historical land that was named after them) The O'Cathan Clan were chieftains in the Owen Clan.