I don’t know if JLC have “borrowed” from IWC or not, but I once were on a lecture regarding the perpetual calendar how it was built hold by Mr Kurt Klaus.
I must say it was very impressive, and I have nothing but great respect for his work!
There might be worse examples to borrow from…

But I agree with you that preferable is that every Manufacture uses their own, but I guess that “steal, beg and borrow” are more common than we might think…
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Sorry, I could not resist! (Nicolas, please remove this post if it against forum regulations)
Best
Blomman