Archimedes Limited Edition: Perpetual Calendar

I am not 100% sure whether those copper oxidation marks are a Bucherer problem or ...
whether other brands using red gold also show these discolorations. I know they can be polished out with an anti-tarnish cloth containing some cleansing agent. But since those are 18K watches, I am not going to bother to do that now. I will probably do it only before a decision to sell is going to be made. I found that the Archmides Jumping Hour back is pretty visible discolorations and that also the Archimedes Rectangle Automatic has some, albeit fewer.
Interestingly the gold-plated Archimedes Alarm is immaculate. The yellow gold-plating does not show any discolorations.