(a) Within 20 days of the date of service of the petition, the employer shall file with the regional office an alphabetical list, including job titles or classifications, of employees employed in the claimed unit as of the last date of the payroll period immediately preceding the date the petition was filed with the regional office, unless otherwise directed by the Board.

(b) If, after initial determination, the proof of support is insufficient, the Board may allow up to 10 days or until the last day of the “window period” as defined by Section 40130, whichever occurs first, to perfect the proof of support.

(c) Upon completion of the review of the proof of support, the Board shall inform the parties in writing of the determination as to sufficiency or lack thereof regarding the proof of support.