Unter-Birnbaum was formerly part of the German Empire. In the German Empire, the place was called Unterbirnbaum.
The place is now called NN and belongs to Slovenia.
| Historical place name | Country | Administration | Time |
|---|---|---|---|
| Unter-Birnbaum | Austro-Hungary | Cilli/Celje | before the Treaty of Saint-Germain |
| Spodnje Grušovlje | Austro-Hungary | Cilli/Celje | before the Treaty of Saint-Germain |
| Spodnje Grušovlje | Yugoslavia | Celje | after the Treaty of Saint-Germain |
| Unterbirnbaum | German Empire | Cilli | 1941 |
| Spodnje Grušovlje | Yugoslavia | Celje | 1945 |
| Spodnje Grušovlje | Yugoslavia | Socialistična rep. Slovenija | 1992 |
| NN | Slovenia | Slowenien | 1991 |