David, agreed they did not publish until 1 October, as I understand it because they at first considered it no different to the many other hundreds of letters received.
it was probably known about within parts of the news industry, and indeed is believed by many to have been produced by a journalist in the first place.
It adds upp well. The journalists got the authentic letter on the 29th. The murders were performed on the 30th just as he said. After the murders the journalists understood that the letter was authentic and published the Dear Boss letter, giving it a false date, on the 1st (if that is a fact). Why should we think that a hoax letter could have a "correct date"? The whole letter including the date is false, Steve.
So even if the other letter was written 29th September 1888, which as you say is open to debate, there is no reason why the name used in the Dear Boss letter would not be known by quite a few persons.
Naturally the name became known when they read the letter from the 29th. And the whole nation got the name soon after.
So why didn´t they publish the real letter? I would say because it would make the police look incredibly stupid.
It was a warning, giving the right day, location and time. "Beware" he says! And they did not understand it. And therefore they could not print this in the papers!
Yes, this son of a x was really outsmarting the police!
But are we not able to outsmart the killer after 127 years? That is the question.