Amos, the CNN tally includes the superdelegates and automatic delegates who are not bound by primary or caucus votes, and who have declared their choice-
463 Republican delegates (123 are automatic delegates) of 2380 total and 796 Democratic superdelegates of a total of 4049 are not bound by primary or caucus vote. Some have announced their intentions and these are included in the CNN count. These people are influential party members, some are members of Congress, etc.
In South Carolina, two superdelegates have announced for Clinton, as I noted in the previous post.

Of course these superdelegates may shift after they find out which way the wind is blowing. Somewhat of a wild card that becomes important when floor votes at the conventions are close and electability becomes the major consideration.

On the Convention floors, 1191 votes are needed to get the Republican nomination and 2025 at the Democratic Convention.
At the primaries and caucuses, 1917 Republican delegates and 3253 Democratic delegates are determined, and are held until released by the candidates whom they represent.

But don't forget these 463 unpledged Republican delegates and 796 unpledged Democratic superdelegates.