GOV § 23289

After the county boundary change is effected, the officers of the accepting county shall proceed to complete all proceedings necessary for the assessment or collection of the state and county taxes for the current year, in connection with all the property in the transferred territory, and, subject to Section 23286, all acts and steps taken, by the officers of the transferring county prior to the date when the boundary change was effected shall be deemed performed by the officers of the accepting county for the benefit of that county.