[1] He had a short hiatus from 1959 to 1960, when he was the director of Statens bygge- og eiendomsdirektorat.
[2] He had applied for the position in the Ministry of Finance in 1951, when Friedrich Georg Nissen was to be succeeded, and all deputy under-secretaries agreed that he was the best qualified among the applicants.
However, Sigurd Lorentzen was chosen, by Minister of Finance Trygve Bratteli.
[3] In 1957, both Grøstad and Lorentzen applied to become the successor of Nissen as permanent under-secretary of state.
[4] In Det nordiske administrative forbund, Grøstad was the president from 1963 to 1971, and later an honorary member.