Well whatever, I bought it as 19th C for a bargain price, and have no particular investment in it being 18th C, I took it in for one of our meetings and was very pleased to hear the opinion that it was possibly older.
Even the best can make mistakes, but they have a world level collection for reference, and the advantage of handling it. I will leave it to you to contact them and inform them of their mistake.
http://www.royalarmouries.org/visit-...eeds-galleries