Actually UW, there're probably enough records to pull out that info from the database, but affiliate stats are a whole other unerverse
The lack of retention stats for affiliates is present not only in NATS
So far, I haven't seen a single (non-CCbill) system that says: you have 10 signups, 2 of them rebilled for 3 months or something like that, not to mention the fact that many stats system don't make any difference between conversion and rebill, so 3 rebills can actually mean 3 conversions from trial to monthly. You need to have the stats listed day by day and track manually what is what and in the end your calcs may not be 100% correct
Andrew