This article suggest they are

http://www.nytimes.com/2008/02/17/business/17swap.html?_r=2&dlbk&oref=slogin&oref=slogin

"But during the credit market upheaval in August, 14 percent of trades in these contracts were unconfirmed, meaning one of the parties in the resale transaction was unidentified in trade documents and remained unknown 30 days later. In December, that number stood at 13 percent. Because these trades are unregulated, there is no requirement that all parties to a contract be told when it is sold."

But with settlement platforms such as DTCC

http://www.dtcc.com/

having been around for a while, is this still the case. With a large percentage of dealer to dealer trades going over the IDB's (Inter dealer brokers such as Creditex), this stuff being automatically settled, and the majority of the rest of the sell side trades automatically being settled, I'm not sure where the number comes from