3rd April 1920
perf †, wmk lozenges
|German stamps of 1906-20 overprinted|
|5 pfennigs green||1||1|
|other values 10pf to 3 marks||2-14||2-14|
† perf 14, 14½, 14x14½, 14½x14
|1920 Sc15 SG15|
In a plebiscite following the 1919 Treaty of Versailles, the residents of this area of East Prussia voted 98% in favour of remaining part of Germany. It was occupied by Russian troops at the end of WW2 and became part of Poland, renamed Olsztyn.
The same set of stamps but with a different overprint (see right) is listed sequentially by Scott  (Sc15-28) but dated May-June 1920 by Gibbons  (SG15-28). Colour and shade variations are noted in both sets.