JFET I drain vs V gate to source curves
Idss is what is different. Idss is a characteristic of the individual JFET, much like hFE of a BJT varies from one unit to the next, and much like hFE the JFETs are 'binned' into three broad ranges so your circuitry does not necessarily have to deal with the entire roughly 10:1 range (the 2.6~20mA range only applies at 25 degrees C junction temperature).