Koetsu Father vs. Sons Old vs. New???????

Well, I guess, there is no real answer.
I read an ad some time ago, there was an very old Koetsu offered and to raise the chance to sell, it was written, that the "Old" ones are the much better ones.

Cartridges have a aging and so it is impossible to answer that correctly and the from the new Koetsu's are so much models and their upgrades available, that you will have problems to compare even "new" with "new".