Do light or non-existent blood drops at the beginning of the menstrual period (which ranges between 13 and 15 days) count as istihadah, thereby permitting prayer, fasting, and sexual intercourse, or are they also considered menstruation?

If the duration of bleeding does not exceed fifteen days, and the period of purity between two bleeds exceeds fifteen days, then all that a woman sees is considered menstruation. If the bleeding stops and she sees dryness, she performs ghusl, prays, and her husband may have intercourse with her. If the bleeding returns, she reverts to being in a state of menstruation.