On page 12: "For some reason (mistake? a tracking attempt?) the account received a tiny amount of 1 Satoshi [...] almost a year later on July 23-rd 2012. Its owner noticed this non-zero balance one year later, and emptied it once more on August 6-th 2013. On September 11-th 2013 he received another tiny transfer of 0.0000091, and on November 18-th 2013 yet another one of 0.00011. On November 20-th he sends the 0.0000091 but the 0.00011 is still there."

Could these be rewards for transaction confirmations? (Probably not since it's not suggested in the paper, and they're the experts and I'm not).