As I wrote in October 2013, an extended TCO is nothing new for sports facilities. Yankee Stadium got its Final Certificate of Occupancy in March 2012, after nearly three years, which is faster than Barclays, but Citi Field, which also opened in the spring of 2009, got its document in July 2013, more than four years later.
What is arena waiting for?
No, it's not easy to figure them out, though in the past unfinished retail space was clearly part of the total. I asked DOB and was sent a link to the page highlighted below, which actually indicates 25 open items of of 140 required.
Most but not all of the requirements seem to be document signoffs, as they can be resolved by documents presented to clerical staff (see "N"). A few others ("T") must be reviewed by a plan examiner.
Some of the latter may have been accomplished but are not fully complete, including seemingly significant items like sprinklers and smoke detection. Also note pending approval for "green roof acoustical wall," which remains under construction.
As the document below indicates, the 9/14/12 TCO indicated unfinished retail.