By default, classes can only be booked within the validity period of the pass. The only reason why bookings outside the pass period can exist, e.g. before the pass starts or after it expires, is because the pass has been manually edited by the studio and the validity period has been changed (see Edit pass of a customer).
Existing bookings of a pass are not automatically canceled by manually changing the validity period. It is therefore recommended that you check and, if necessary, cancel bookings that are outside the newly entered validity period.