They want to make sure that you APH yields are correct for the last 3 years. You just need proof of how many bushels you sold or feed and that needs to match up with the yields you gave them. If you are short bushels I think they just lower your APH yields for the year or years that you were short. If you only have one crop that goes over the $200,000 limit then that is the only crop that gets audited. If both corn and soybeans are over the limit then they will both get audited unless they change the rules before fall.