20 CFR 404.1215 - Modification of agreement.
(1) Exclude, in limited situations, employee services or positions previously covered;
(2) Include additional coverage groups; or
(3) Include as covered services:
(i) Services of covered employees for additional retroactive periods of time; and
(ii) Services previously excluded from coverage.
(b)Controlling date for retroactive coverage. A State may specify in the modification a date to make all individuals in the coverage group who were in an employment relationship on that date eligible for retroactive coverage. This date is known as the controlling date for retroactive coverage. It can be no earlier than the date the modification is mailed or otherwise delivered to the Commissioner nor can it be later than the date the modification is signed by the Commissioner. If the State does not designate a controlling date, the date the modification is signed by the Commissioner is the controlling date.
(d)Effective date. Generally, a modification must specify an effective date of coverage. However, the effective date cannot be earlier than the last day of the sixth calendar year preceding the year in which the modification is mailed or delivered by other means to the Commissioner. The modification is effective after the effective date.