Unfortunately, there is no way of knowing, even using a 3rd party processor such as CCBill it is possible to shave webmasters extremely easily.

Its as simple as setting a maximum rebill limit on affiliate accounts using CCBill.

Id figure, the industry average for rebills is somewhere between the 2-4 month period if you have a reasonable site, you can quite easily set the rebill period for which affiliates are credited to 3 months and they'd be non the wiser.

Regards,

Lee