IWEC vs IWEC2 weather files

Hi all!

Is anyone here familiar with the differences between EnergyPlus IWEC and IWEC2 files?

I understand that the calculation model which is used to interpolate the global radiation in the IWEC2 file has been updated.

I've been running some comparison tests between IWEC and IWEC2 for Stockholm, Sweden, and the differences are causing me some concern. For example, the maximum radiation on an unshaded south-facing vertical surface is

781 kWh/m2 with IWEC, but
960 kWh/m2 with IWEC2.

I downloaded the IWEC file from DOE's webpage, and the IWEC2 files are purchased directly from ASHRAE, so they are both reliable.

In previous projects that I have done I have used the IWEC format and thought it to be quite reliable, the results even compared quite nicely to simulations done with IES VE (which gave 811 kWh/m2 on a unshaded S vertical surface).

IWEC2 is the current official format of ASHRAE's epw weather files, so they should be pretty reliable. This large difference between IWEC and IWEC2 is however giving me doubts on if either of them are safe to use.

Please share your thoughts!