This is a question regarding the economist and political thinker Ludwig von Mises.
A short biography: Mises was born in 1881 in Lviv, then part of Austria–Hungary. He studied and worked in Vienna from 1900 until 1934, when he moved to Geneva, Switzerland (this was, I believe, due to the rise of Nazism in Germany and Austria; Mises was Jewish). In 1940, Mises moved to the United States, and became a US citizen in 1946. He lived in New York until his death in 1973.
Mises is sometimes described as having been of Austrian nationality; the German Wikipedia page, for example, says that he was an “österreichisch-US-amerikanischer.” But if Mises had in fact been an Austrian citizen, he most likely would not have been able to retain the noble particle in his name (von) when the Austrian nobility was abolished in 1919. (Friedrich Hayek, an Austrian citizen, was called Friedrich von Hayek prior to 1919.)
After the fall of the Austro–Hungarian Empire in 1918, Lviv (Mises’ place of birth) became part of Poland and remained thus until 1945, when it was annexed by the Soviet Union and integrated into Ukraine. Was Mises perhaps a Polish citizen during that same period, and could that explain why his name remained unchanged?