The paper mentions that the metadata includes ISO Alpha-3 country codes (Appendix I). However, the country_code field in the metadata json's includes two codes that do not exist as ISO Alpha-3 code: KO- and CA-.

• KO- is not listed as any country code on the ISO website. KO is listed as unassigned Alpha-2 code: link. All locations in the fMoW dataset with this country code are in Kosovo. Kosovo does not have its own ISO Alpha-3 code, the correct code is the one for Serbia: SRB (just quoting the ISO website). There is an unofficial Alpha-2 code for Kosovo, as described here; XK.
• Same for CA-, it does not exist as Alpha-3 code. CA exists as Alpha-2 code for Canada (ISO website), but the fMoW metadata uses the Alpha-3 code CAN to refer to Canada. The locations in the fMoW dataset with CA- are around the Caspian Sea, both in southern Russia (Dagestan) and Azerbaijan. I don't know why the proper codes, like RUS or AZE wouldn't be used. Some of these locations are in Azerbaijan's capital, so doesn't seem like disputed territory.

I'm posting this here not to get political but because I think this might be relevant to some people, and it is poorly documented by fMoW. E.g. I was trying to connect the fMoW countries to ISO 3 country codes in a shapefile to do operations with the locations. Please document this properly somewhere :-).