The effective date is the "cover" date of the search on which the title insurance commitment is based. The cover date is the date through which the courthouse records were available.
For instance, let's say the abstractor goes to the courthouse to do the search on July 15 but the available records in the Recorder's office are really behind - perhaps only indexed through June 30. [That really would be terrible, but it happens.] The cover date of the search and the effective date of the title insurance commitment would be June 30 even though the physical search took place on July 15.