Problem is that the Isc is very dependent on the solar irradiation. The 48
Watts are defined under STC (standard test conditions), o.a. 1000 W/m2
irradiation, defined spectrum and at 25°C.
In my opinion it is not straightforeward to test the quality of the panels.
I don't know for which you are using them. But if they deliver enough power
most of the time, it iis still OK. When you run "always" out of power,
either minimise your power consumption :-) or replace he modules (or add
additional panels to them).