Not all discussion posts get a grade. Posts that are graded usually get some portion of the total discussion points for the topic.
The sum of all individual post grades may be greater than the total for the entire discussion. There are frequently extra points for early posts, good questions, helpful responses to other students, interesting additional information, … anything that makes this online learning community a better experience.
Occasionally I miss a post that should receive a grade. If you think this is the case, please bring it to my attention.