Conn. Gen. Stat. § 12-263d

(b) Except in the case of a wilfully false or fraudulent return with intent to evade the tax, no assessment of additional tax shall be made after the expiration of more than three years from the date of the filing of a return or from the original due date of a return, whichever is later. If no return has been filed as provided under the provisions of section 12-263b , the commissioner may make such return at any time thereafter, according to the best information obtainable and according to the form prescribed. Where, before the expiration of the period prescribed herein for the assessment of an additional tax, a hospital has consented in writing that such period may be extended, the amount of such additional tax due may be determined at any time within such extended period. The period so extended may be further extended by subsequent consents in writing before the expiration of the extended period.

(c) The commissioner may enter into an agreement with the Commissioner of Social Services delegating to the Commissioner of Social Services the authority to examine the records and returns of any hospital subject to the tax imposed under section 12-263b and to determine whether such tax has been underpaid or overpaid. If such authority is so delegated, examinations of such records and returns by the Commissioner of Social Services and determinations by the Commissioner of Social Services that such tax has been underpaid or overpaid shall have the same effect as similar examinations or determinations made by the Commissioner of Revenue Services.