Non-International currency

Example: I have a 25,000 Non-International currency has value set at 4,000 usd when I go into China years later when I leave and going to Hong Kong the country of original currency has now become an International currency worth 100,000 usd. What do I do? I did not declare the currency going into mainland because it was under the 5000 usd value.

I travel a lot I am unclear on customs. What ever you declare as long as documents with proof of legal. You can declare 1000000 usd you get to keep it, right?

Thank you so much whoever responds....