Earlier quoted context omitted.
The article is not correct on salaries being public: What is public are your tax reports and those are done a year later. To my knowledge you cannot see all details either, only totals that the tax is based on. Thus I think your statement is wrong or at least it is not related to the public databases mentioned in the article.
The full social security number for a person is not easily obtained and not published by the free websites.
I have needed to provide information for a visa application including family history on dead half-relatives from a branch of the family tree I have very little contact with. It was a breeze. Names at birth, later marriages, dates of death and everything that I had no idea was given without delay (as stipulated by law).