California Code, Business and Professions Code - BPC § 7125.5

(a) At the time of renewal, all active licensees with an exemption for workers' compensation insurance on file with the board, submitted pursuant to subdivision (b) of Section 7125, shall either recertify the licensee's exemption by completing a recertification statement on the license renewal form, as provided by the board, or shall provide a current and valid Certificate of Workers' Compensation Insurance or Certificate of Self-Insurance, whichever is applicable.

(b) The license shall not be renewed unless a licensee with an exemption for workers' compensation insurance on file with the board recertifies the exemption status or provides a current and valid Certificate of Workers' Compensation Insurance or Certificate of Self-Insurance in conjunction with the license renewal.

(c) If the documentation required by subdivision (a) is not provided with the license renewal but is received within 30 days after notification by the board of the renewal rejection, the registrar shall grant a retroactive renewal pursuant to Section 7141.5 back to the date of the postmark of the otherwise acceptable renewal.  A renewal that is still incomplete for any reason after 30 days after notification of rejection shall not be eligible for retroactive renewal under this subdivision.