I think the data for Dec 31 1980 for wind europe is missing.
Dear Tarjei,
I see that december 31 1980 is indeed missing in the (individual) country wind datasets, which contain wind capacity factors. Wind dataset 1.1 also offers hourly data for wind capacity for European countries, and looks complete to me, including december 31 1980. This dataset is available at https://www.renewables.ninja/downloads
If you want a complete dataset I advice to download v1.1, or else wait for a reaction of the renewables.ninja team.
Kind regards,
Hans Cappelle, Belgium
FYI: some (wind) plots from renewables.ninja data-set 1.1 for Europe are available at