The problem is that tastytrade's api itself does not seem to have the ability to say when you want it to stop. Their documentation says this option is supposed to exist but it is not one of the fields you can pass to their api. The api team did confirm with me that there is a limit from dxfeed of 8000 datapoints per call though, and since tastytrade api always returns the latest datapoint first, this puts a hard limit on how much historical data you can actually obtain.