the period of plan qualification with respect to the employer will begin on the date the plan is adopted by the employer (or, if later, January 1, 1977). If the form and schedule are not filed before the latest of the dates described in subdivisions (i), (ii) and (iii), the period of plan qualification with respect to the employer will begin on the date of filing. In any case in which either the Form 1024 or Schedule L filed by or on behalf of an employer is incomplete, the date of filing is the date on which the incomplete form or schedule is filed, if the necessary additional information is provided at the request of the Commissioner within the additional time period allowed by the Commissioner. If the additional information is not provided within the additional time period, allowed, the date of filing is the date on which the additional information is filed. If no separate Form 1024 and Schedule L are required to be filed by or on behalf of an employer (see paragraph (b)(3) of this section), the period of plan qualification with respect to the employer will begin on the date the plan is adopted by the employer (or, if later, January 1, 1977). In any case in which a plan is materially modified to conform to the requirements of section 120, either before or after a Form 1024 and Schedule L are filed, the period of plan qualification will not include any period before the effective date of the modification.
26 C.F.R. §1.120-3
Secs. 120(c)(4) and 7805 of the Internal Revenue Code of 1954, 90 Stat. 1926, 68A Stat. 917; (26 U.S.C. 120(c)(4) , 7805 )