Ahh, yes, the 1c payment. I believe it's per 1000 impressions, and it accumulates over days or weeks, and once some specific ad has been on the page long enough to receive the 1000 imps, you get a cent.

Unfortunately, there is no indication that you get it (other then the 1c referral fee), and no indication for what ad, etc. The only way to see it, is to view your report before you get any clicks, and already have that 1c. So you might have had them before, and just not noticed them 'covered over' by click revenue.