This is true - and readily admitted by HK dealers.
The explanation is that one set of hands matches a dial better than its originals, and so on.
So these very fine, matched patina watches are possibly, perhaps probably, mixtures of many watches of the same reference - assembled to produce, as said above, a quality line from top to worst.

 

I suppose this is just a step up from changing an insert over on a Speedmaster or bezel on an SM300.

 

For the sake of argument, as long as all parts r period correct n look good, why not? We do it all the time with cars, why not watches. I dont prefer it but im sure some of my watches r not all original.