[mzs]

zoneinfo does in practice hold the historical info before 1970 when it can do so easily in its framework: https://en.wikipedia.org/wiki/UTC%2B01:24

  % zdump -i Europe/Warsaw | head
  
  TZ="Europe/Warsaw"
  - - +0124 LMT
  1880-01-01 00 +0124 WMT
  1915-08-04 23:36 +01 CET
  1916-05-01 00 +02 CEST 1
  1916-10-01 00 +01 CET
  1917-04-16 03 +02 CEST 1
  1917-09-17 02 +01 CET
  1918-04-15 03 +02 CEST 1
  % zdump -i Europe/Kaliningrad | head -20
  
  TZ="Europe/Kaliningrad"
  - - +0122 LMT
  1893-03-31 23:38 +01 CET
  1916-05-01 00 +02 CEST 1
  1916-10-01 00 +01 CET
  1917-04-16 03 +02 CEST 1
  1917-09-17 02 +01 CET
  1918-04-15 03 +02 CEST 1
  1918-09-16 02 +01 CET
  1940-04-01 03 +02 CEST 1
  1942-11-02 02 +01 CET
  1943-03-29 03 +02 CEST 1
  1943-10-04 02 +01 CET
  1944-04-03 03 +02 CEST 1
  1944-10-02 02 +01 CET
  1945-04-02 03 +02 CEST 1
  1945-04-10 00 +02 EET
  1945-04-29 01 +03 EEST 1
  1945-10-31 23 +02 EET
  %

[inglor_cz]

Koenigsberg was conquered by the Soviets in April 1945, but the final Soviet-Polish border was only established in August of the same year. I wonder when the official switch to EET was made. For several months, the future of the city was a bit uncertain.