Short answers, pulled from the story.
Geoffrey Chaucer was the first poet interred in Poets' Corner, buried there in 1400. His burial was owed to his position as Clerk of Works at the Palace of Westminster rather than to his literary reputation.
Byron died in 1824 but received no Poets' Corner memorial until 1969, a gap of 145 years. His poetry was widely admired, but his lifestyle was considered scandalous by those who controlled access to the Abbey.
Ben Jonson is not buried in Poets' Corner. His grave is in the north aisle of Westminster Abbey's nave, inscribed "O Rare Ben Jonson." A separate wall tablet, designed by James Gibbs and carved by John Michael Rysbrack, was erected in Poets' Corner in 1723.
Hardy's remains were split between two locations. His heart was buried at Stinsford on the 16th of January 1928, as he had wished, while his ashes were interred at Westminster Abbey after his executor, Sir Sydney Carlyle Cockerell, insisted on a Poets' Corner burial.
The Poets' Corner stained glass window was unveiled in 1994, in memory of Edward Horton Hubbard. It holds room for 20 names, and the most recent addition, Elizabeth Gaskell, was unveiled on the 25th of September 2010.
Dickens's will stipulated that there be no grand funeral ceremony. The Abbey honored this instruction with a secret early-morning interment on the 14th of June 1870, before the public could gather.