I see that you're now comparing two datasheets of diodes from different manufacturers, GB02SL...& C4D021...? And all can withstand 1200v Vrrm. But the maximum forward current, I-f for the GB021.. is 2A while for the C4D021.. is given as 6.9A, right? The different makers here are claiming different ratings for their devices and that is not your problem, right? You have a problem where the makers are quoting the voltage drops across the diodes, right? These Vf ratings are given as 1.75v max at a sampling current of 2A when measured at 25 deg for the GB021.. diode whilst the Vf for the C4D021 is given as 1.8v also at a sampling current of 2A. May I add that these are the maximum voltages that are lost across the diodes as they carry load current. It is just a standard here that they are compared as they carry only 2A, which happens to be the maximum forward current of the GBO21 diode. Is this clear?