The 7th Bureau and the 7th Secretariat of the Russian Communist Party (Bolsheviks) were elected by a Session of the 7th Central Committee in the immediate aftermath of the 7th Congress. The 7th Orgburo was elected by the twenty-fourth session of the 7th Central Committee, held on 16 January 1919.
References
7th Bureau, the 7th Secretariat and the 7th Orgburo of the Russian Communist Party (Bolsheviks) Wikipedia(Text) CC BY-SA