(a) Within 20 days of issuance of a notice of intent to conduct election, the employer shall file with the regional office an alphabetical list, including job titles or classifications of employees employed in the appropriate unit, as of the last date of the payroll period immediately preceding the date of issuance of the notice of intent to conduct election, 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 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.