Service to SEZ

We need to look at the Central government notification confirming the SEZ status. We normally take a letter from the client confirming that they have SEZ status, the effective date from which they have this status & that as per the notification service tax does not apply to the specifiic service that they are taking from us. The Service tax exemption will apply only from the date of the notification. So, if any service is rendered before they get this status, service tax will be apply. So, effective date is an important factor.