To be honest, the ammo and labeling at the beginning from the Plant Skarzysko-Kamienna is a little confusing to me.
The plant was occupied in 1939. Hasag (Hugo Scheider A.G) used there good connections in Berlin and together with a company called Rochling they took over the temporary management of the former PWU. From August 1941 alone and HASAG buy the plant in 1943.
There are German boxes known packed with 15 round S and sS bullets
Inside, a mix of Polish rounds from 1928 until 39. The box is only stamped with “S, oL Polnish” and “SC,oL Polnisch”
The first HASAG head stamp (2e Lot of 1940) is packed in a box with only a printing “Fr Gewehr” on top. No further label.
In 7.9 there are only sS (heavy ball) cn plated bullets from 1940 known.
The first SmE (lead replaced by an iron core) is known from 1941. They were still made with Polish materials. (cn bullet). If a factory used non German material, the round was not made to German specs. It could be the case, powder, bullet or primer. It was printed always on the label like (f), (b), (h), (p), (t), and so on.
The first German sS bullets came from P491 and later they made the SmE bullets by there self.
In 1943 the rest of the Polish brass cases were send to Germany were they made blanks of them.
Hope I could help a little
Rgds
Dutch