Update for my C23 support case with Yuneec Europe.
The new C23 arrived yesterday and it is indeed brand-new (different serial number, new camera with lens sticker on) as it does not have the (really small but noticeable) marks on it's case (my original C23 came with them but did not affect it's operation). Flew it with my Typhoon H+, perfect footage without jello. The camera has also the latest Build 822 firmware, so everything was perfect right out of the box.
I have to give extra credit to Yuneec Europe for their professional attention to the case; although my machine was out of warranty, they've replaced the C23 with a new one. This is something you do not get from other companies (in particular dji which I had to deal with them in the past), I do not know if it had to do with the fact that I bought my drone from them but for me they came through with flying colors.