This set of Germania overprints was issued on 12 May 1915, and bears the overprint “Russisch Polen” (Russian Poland).
This set was issued on 1 August 1916, and saw a switch to an overprint of “Gen-Gouv. Warschau”.
Shown below are the stamps of the GermanStamps.net Collection on the physical album pages.
This area of Russian Poland was placed under German administration as the “Generalgouvernement Warschau” (General Government Warsaw).