Hi Anna,
Thank you; this is great for clarification! Each competency statement in total should be no more than 500 words. So, CS I altogether is no more than 500 words. So CS I a + CS I b + CS I c = 500 words. The CDA book you received should also explain the competency statements in more detail- somewhere around page 17, depending on age level.
I hope this helps, and don't hesitate to reach out if you have further questions.
All the best!