When Does “1984” (1949) Take Place?

"Nineteen Eighty-Four" (sometimes released as "1984") is a political science fiction novel written by George Orwell a.k.a. Eric Arthur Blair that released June 8th, 1949. 

It takes place roughly in the year: 

~1983 AD or 1984 AD 

We think we know this because (beyond it being the title on the cover [peritext]) very early in the story Winston Smith writes an entry in his diary and begins it with "April 4th, 1984". 

HOWEVER, the government tells everyone it is 1984 AD but, over the course of the novel, evidence increasingly mounts up telling the characters that they cannot trust their government. As the proper trust in society is lost so is a proper sense of time and characters have concluded they do not know what year it is. "Everything faded away into a shadow-world in which, finally, even the date of the year had become uncertain." 

Even just after Winston wrote the date at the top of his diary the narrator tells us, "A sense of complete hopelessness had descended upon him. To begin with, he did not know with any certainty that this was 1984. It must be round about that date, since he was fairly sure that his age was thirty-nine, and he believed that he had been born in 1944 or 1945; but it was never possible nowadays to pin down any date within a year or two." 

1944 + 39 = 1983 

or 

1945 + 39 = 1984. 

More specifically, the book opens with the words: "It was a bright cold day in April, and the clocks were striking thirteen." and very soon that's followed with "the cold of the winter that had just ended." So, presumably, it's April of 1983 AD or 1984 AD. 

It was adapted to television in 1953, again in 1954, to film in 1956, again to television in 1965, then to film again in 1984, to comics in 2012, to the stage in 2013.