The only time I've seen them last longer than 30 days, is when the device happens to have a custom policy applied to it. In that situation where it still shows up in the 'Clients with a Policy' page, it always says 'Device removed from network'.
this its because I need the data for create reports, however, in my reports they ask me for an interval of at least 10 minutes, it is possible that the api will refresh the data of the traffic of the users who connect to my Access point in that interval, since I visit pages but it does not show me changes. API as such, I thank you very much in advance for your valuable answer.
Looking at this on a wider view, there is no way to clear statistics on a network without creating a new network and moving the appliance. Sometimes you just want a fresh look. As a Enterprise Administrator the ability to do this would be helpful.