Both Henderson and Dingee & Conard were exhibiting it in 1891 (at the 7th Annual Convention of the Society of American Florists at Toronto, August 18-21, 1891), should that have any implications as to who actually introduced this rose.

Just incidentally: The "Wm. Falconer" in some of the references was himself to be a figure of great note in American horticulture. Trained at Kew, known to Hooker, and then in America known to Sargent, etc. etc. I've understood that HMF doesn't allow links; but Google "William Falconer botanist" and much info on him will be found.