I cannot verify any of this. But it is a bit ironic that @Kathy_Lewis posted this the other day: Recreation of an Infusionsoft "Referral Partner Activity Summary".
Kathy is doing the same thing as you in logging the information in the database, but there is differences between what is being reported.
The problem is that we do not have full Infusionsoft database access, so we do not know how the information is being stored and generated.
There is something that springs to mind though. If you are storing the data in your own database, then how does it deal when Infusionsoft Contacts and other records are either modified, merged or deleted? Then you will start seeing some differences between your data and Infusionsoft.