Effectiveness rates for any method of birth control are based on one year of usage, not on any specific incident of sex. For the combined pill, this does include times when a partner ejaculates inside of you. These rates are based on using one method alone, and do not take into account increased protection from using another method.
For more information about the combined pill, you can read: Combined Oral Contraceptives (The Pill)
For information about effectiveness rates combining two methods, you can read: The Buddy System: Effectiveness Rates for Backing Up Your Birth Control With a Second Method