It is a good idea to start small; a small group of records and only one value. If only to be able to fix things by hand without too much trouble. One bug found, fixed and up to the next challenge.
The presidents of Argentina probably are also likely members of a party so they were next. No record changed, so I checked Juan Perón to find that he was a member of the Justicialist party.
I found another bug. This bug is now being fixed as well; people are really helpful. Probably they want more data in Wikidata as well.
PS I have also done some work on the "kings of Nekor"