7,92x57 lacquired cases

I have some 7,92x57 cases and Platz 33 cartridges wich had additional lacquering with transparent brownish varnish above copper platted steel case. For example:
fired case with marked P491 VIIc1 4 39
Platz 33 with headstamp P198 VIIu1 13 38
Platz 33 with headstamp am VIIg1 134 40

Some of this specimens have reloaded mark, and some - no.
What does this varnish means? May be it was transition variant of cases before start of producing steel cases with green varnish? Or may be it was a special covering for improvement the removing fired cases from the barrel in non-automatic weapon?

While Mr.Treshkin is waiting for an answer, I’ll segue a related question. What is “VIIIc1”?

The combination of Roman Numeral, letters and Arabic numbers is a steel analysis code. It has been explained before on this Forum, in fact one quite recently.

The Roman Numeral identifies the steel mill supplying the first-draw cups to the case makers. In this instance “VIII” identifies Dortmunder-H