It appears that the 19th LD were issued with the new Frenchified dragoon headdress and uniform either shortly before their arrival in North America or shortly after they arrived. This was in contrast to the Cdn dragoon units who retained the older style of dress with the Tarleton helmet (so named after the hero of the Revolutionary War).
The 19th LD of the Napoleonic period are well covered in their regimental history by John Biddulph, THE NINETEENTH AND THEIR TIMES: BEING AN ACCOUNT OF THE FOUR CAVALRY REGIMENTS IN THE BRITISH ARMY THAT HAVE BORNE THE NUMBER NINETEEN AND THE CAMPAIGNS IN WHICH THEY SERVED (London: John Murray, 1899), one of the better British cavalry regtl histories.
Lieutenant John Lang of the 19 LD kept a diary of his service in North America and it is presently in the Perkins Library of Duke University in Durham, NC.
Interestingly enough, one of the 19 LD officers who served in North America during the W1812 was Lieutenant William Arnold, son of Benedict Arnold, that outstanding servant of the Crown in the Revolutionary War.
Cheers
DG
DE Graves