There was another letter very similar to Dear Boss, Saucy Jack and especially Moab and Midian that was written in october of 1889. Interestingly it was addressed to Albert Bachert, again, and denied claims (most likely to the Pinchin torso) just as M&M denied claims to the Whitehall torso.
Whitechapel, Oct. 11, 1889
I write you these few lines to let you know, as you are the boss of the vigilance committee, that the last job was not me. You might have known it was not me, for I would not have made such a botch of it. Never mind, young man; you can keep your lamps open for the 18th of October. I am on the job again. There's no blood knocking around or I would let you see some. Never mind; look out, old man, you're a brave sort. You thought you had me once. Yours in haste,
Jack the Ripper.
A side note about Bachert is another letter was received by him (Eastern Hotel POP letter) that the original was destroyed and due to Bacherts skills in engraving he transcribed the letter in similar handwriting.
Woodford Times (Essex)
Friday, 19 July 1889
LETTER FROM "THE RIPPER."
As a corroboration of the above theory, and justifying the action of the Thames police, a letter was received a few days ago by Mr. Albert Backert [Bachert], Whitechapel, as chairman of the vigilance committee, commencing: "Eastern Hotel, Pop-." And then thickly penning the words out. Mr. Backert states that he was urged to treat the matter as a practical joke; but in view of the writer "Jack the Ripper," threatening to re-commence operations about the middle of July, and Wednesday morning's murder, inquiries have been made, with the result that it has been discovered that there is an Eastern Hotel in the East India Dock-road, Poplar, which is within a stone's throw of the docks, and where a number of sailors put up. It is thought probable that the murderer may have been on a voyage during the interval between the Miller's-court murder and the one which on Wednesday renewed the horrors which have shocked the world.
July 27, 1889
As a preliminary, however, he tried to obtain from Baeckert a specimen of the handwriting in which the letter signed Jack the Ripper was written. Though he failed in this owing to the letter having been destroyed, Baeckert who was an engraver by trade and so was accustomed to imitate what he had seen reproduced for what it might be worth a specimen of the writing as he remembered it.