The Wiki is claiming that the Dune Calendar starts with the Spacing Guild. Is this and their analysis accurate? If not then:
Can we say by our calendar when is 10191 in the Dune universe?
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From the wikia that you linked:
Thus, the year 10,191 AG corresponds to the year 21,267 A.D. That is, of course, assuming that the Dune chronology actually uses Earth years.
But Dune counts in Standard years:
"Taraza was momentarily abashed. This was an imposition. Teg was still a regal figure, tall and with that large head topped by gray hair. He was, she knew, four SY short of three hundred. Granting that the Standard Year was some twenty hours less than the so-called primitive year, it was still an impressive age with experiences in Bene Gesserit service that demanded that she respect him." HoD ~Page 36 So there could be a maximum error of about 400 years (since we do not know when the Dune Universe started using the "Standard" year). This method also assumes that humankind began exploring "deep" space in the 20th century a decade after World War II.
So accepting all those assumptions it would be between 21,267 A.D. and 21,667 A.D.
I think the year 10191 comes from the Dune movie (1984). I can not recall having read this in the book, though I may be wrong. Because it is harder to create the entire Dune universe in a movie, they may have used Earth years instead, so 10191 is 10191 AD. This would make sense, because the film introduction by the princess also claims that "The Spacing Guild and its navigators, who the spice has mutated over 4000 years (...)". Since the Guild only has a place in the universe with Guild Navigators, the Guild can not have been much older than 4000 years in the year 10191.
The novel DUNE is set twenty five thousand years from now.
The year 10191 isn't using our existing Gregorian calendar.
We are now at around 14300 years BG (BEFORE GUILD)
14300 years from now the guild and CHOAM are established.
The calendar is reset at this time. Years are now AG (AFTER GUILD)
I Assume old Earth years are still used with this new calendar (365days).
10191 Years later are when the events of Dune take place.