I thing, those date are correct..
Before german ocupation on Polish (small) coast wasn't any german unit, city or harbour...
This is no big problem, but Gdynia was build in 1920-30th from very small fishing vilage to big sea port whith about 200k peoples in 1939.
Somewhere above 1938 Gdynia has the bigest reloading goods on Balitic Sea.
We can search for Polish coast map from that time and web materials.
Greatings from Gdynia
Jack_410 & Epyon
ps.
Gdansk (Danzig) before war was set by Nation Ligue as Free City of Gdansk and theoreticaly it nor belong to German nor to Poland
Practicality Gdansk was dominated by german peoples, who make big troubles to polish trafic, exclude Poland from sea.
It give rise to build Gdynia as independent from german polish port/naval sea base city.
Even in Gdansk to september 01 1939. there weren't any regular German land/air unit, there was only Police, and from august 25,there was German shool battleship Shlezwig-Holstein know as a starter of second world war. There was also one Polish company in Westerplatte (Polish transit station on entrance to port Gdansk) and they were defending they position for 7 day without any suport.
Polish naval base Hel (4x152mm Bofors etc.) fight to october 01 when the Polish rearadmiral Unrug ordered capitulation of last polish soldier in polish coast.
Verry Sorry for history lesson.