Your favorite credit card has sat in the top pocket of your wallet for years. You have memorized the interest rate, the credit limit and its perks. Think you know everything about your favorite credit card?

Not necessarily.

Even if you've carried the card for years, it could have a couple of surprises in store. Card issuers and the government continue to change card rules. Interest rates and credit limits can grow or shrink with your circumstances -- or those of the card issuer. And then there are those uncommon details you may have missed.

But don't stay in the dark. Like any card game, you stand a better chance of holding a winning hand if you know the rules. Here are eight secrets you may not know about the plastic in your wallet.