Sorry, but I don't agree with your logic (or illogic).
In reality, every item for sale has several "purchase prices". The 'original asking'(non-sale) price. The 'actual' sales price. The 'wholesale' purchase price that the wholesaler asked. The 'actual wholesale' purchase price that the merchant (JC Penny) paid, etc. And so on for every sales transaction regarding that item. Which 'purchase price' do you demand?? Why not the original wholesale price??? [The wholesale price fits your logic, but doesn't allow you to abuse the merchant to your advantage.]
The JC Penney agreement doesn't say you get a credit for the original 'price'. It says for the 'original PURCHASE price'.
The "original purchase price" for this transaction is the price that you PAID, not the price that they wanted.
'Purchase' is defined as:
: an act or instance of purchasing: as
a: the acquiring of real property by any means other than descent or inheritance
b: the acquiring of an interest in property esp. in exchange for valuable consideration"
Specifically: ": to take (property) by a voluntary transaction (as a sale, mortgage,
pledge, lien, or gift) that creates an interest and that is governed by the Uniform Commercial Code"
Based on the above, I believe that JC Penny is absolutely correct in allowing a trade-in value equal to your 'purchase price', not the higher 'asking price'.
As in most legal issues, a true telling of the facts can be found by reversing the roles. Let's say that YOU sold me the diamond ring and I returned to YOUR STORE with the same argument that you offer. Would you allow me a 'trade-in' credit higher than I paid??? I don't think so!!!
Judgment Recovery of Houston
This is my PERSONAL OPINION and is not legal advice! Consult your local attorney for your specific situation and laws!