I found an order on zip fasteners that might be of interest. It's a Reichsbefehl from 1936 (still in force in late-1942) and it states that zip fasteners were forbidden on party uniforms. The order is clearly a reaction to the practice of some manufacturers to add zips instead of the regulation buttons. The order specifically mentions the following items as being prone to the practice:
Winterbluse
Skihose
Stiefelhose
BdM Rock
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Interesting, thank you Garry. I did not think about this before but yes, even though zip fasteners existed at that time you do not see them normally on NSDAP items
The pics on this thread and the other one referenced by Henrik are sports shirts or at the very least sports-related. I'd be interested in your zipped Winterbluse Joe because it is a uniform item specifically mentioned by the regulation.