I have made my living for 32 years designing software and working on ergometrics to increase useability and ROI....
LOL I got about a 100 of them....
On the card details in the collection a symbol when you are showing all cards that you have a gold card version of the card (MAYBE A BIG GOLD STAR) And when you are looking at the stats and cards next to the buttons to switch to Alpha, Beta and Promotion there should another to switch to gold!