Solofun

I have a question related to fcc. I have an fcc from a June 20 cruise that was applied to a sept 22 cruise. I always thought they did something wrong in applying it as it’s such an old fcc. Now I want to apply those cruise credits to a different cruise but I worry about losing that cruise credit. It’s also a sept 22 cruise. Am I worrying over nothing? I just don’t want to lose that cruise credit.