It was available on June 30 and July and the litter is referred to as the Server litter.
"Reason: On June 29/30, 2012, there was an enormous storm in Northern Virginia that knocked out CS's server; CS had to be restored from a day-old backup, and everyone was upset at the loss of nearly everything that happened on Friday, June 29, 2012. (That week was jokingly called "The Week with No Friday" for a while.) You can read more about it
here. This litter was released early to help everyone recover from the data loss (and no, June's pets were not taken down early). There is also a news post about it
here)."
Quoted from
this guide