Canadian newspapers mentioned the Promised Messiah AS (and Qadian) as early as 1899.

Newspaper: "The Evening Star"—known today as "The Toronto Star"

Date: Monday, December 4th, 1899

#TarikheAhmadiyyat

Full page of "The Evening Star", with the news item highlighted:

This news was published in Montreal, Quebec (Canada) on the same day.

Newspaper: "The Gazette"
Date: December 4th, 1899

More info:

Prior to this, it was published in London's "The Saturday Review" on Dec 2nd, 1899.

I'm not exactly sure if there were other British newspapers that published it; subsequent publications mainly referenced "London, Dec 2".

(The Saturday Review Archive, v.88 p.696)

By my current count, it was published in at least 58 different newspapers in London, USA and Canada.

Here are some other versions:

1. NY Times (most popular version)
2. Arizona Republican (best/most complete version, in my opinion)
3. The San Francisco Call
4. NY Journal

Here is the entire list of 58 newspapers found so far that published this piece (in London, Canada and USA).

According to this list, it was published from December 2nd, 1899 to June 1st, 1900.

Many American newspapers reported it on December 3rd, 1899.

Also, if you're wondering whether the conference was ever organized & anyone ever accepted the challenge—it wasn't; and no one ever did.

Maulana Dost Muhammad Shahid Sb writes that the world was forever deprived of this golden opportunity.

(Tarikh-e-Ahmadiyyat v2 p61-62)

/end