found:LC in OCLC, Sept. 10, 2004(hdg.: Oldenburg (Grand Duchy))
found:Matheboard.de, website, Sept. 9, 2004 (Herzogtum Oldenburg became Grossherzogtum Oldenburg in 1815; Birkenfeld was added so that now the Grand Duchy consisted out of three regions: Oldenburg, Lübeck and Birkenfeld. In 1918 jurisdiction changed to Freistaat Oldenburg. During this period (until 1946) Oldenburg lost both Lübeck and Birkenfeld.)