I actually did measure the voltage across the multimeter leads on the batch of 350W panels and it was 1.22V for one multimeter pulling 9.6A and .98V for the other pulling 9.8A (same current).
So let's assume there is another 2V across all the other parts of the circuit (probably much lower than that). So, the current (9.5A) should be within 2% all they way to probably 15V, there's no way there was 15V across the leads. So in the case of solar cells, you are measuring the current to within +-2% of a real short circut even if you have a multimeter with a horrible shunt resistor.
Besides, for sake of erring on the side of being optimistic, I just used the measured quasi short circuit current as the maximum power current (which it probably is much less, maybe 10% so) and you will find that the power even optimistically is less than 50% of the specified panel power.
So I give you the point, it would be nice to be accurate, but in this particular circumstance, it's not making a material difference in the conclusion if you have a few volts (< 10V) across the panel when you're measuring for the short circuit current.