I was originally thinking that it would compare the states. So, if all were 1 the answer would be 1.
I forgot that {EXP:({STATE_KEYSTATE:SHIFT} + {STATE_KEYSTATE:CTRL} + {STATE_KEYSTATE:C})} is adding the states together, if all are pressed, they add up to 3, but if you have Shortcut is invoked when all keys are released check, the answer is 0. That's why my answer was 0. If you don't have the shortcut invoked box checked, the answer will be 3.
Also, I checked, and it doesn't seem to matter how long you hold the keys before release, it doesn't appear to have any effect on the Shift key. The command seems to always work as you wish it too.