In ascertaining the assets, liabilities and financial condition of all other insurance companies, not otherwise provided for in sections 44-401 to 44-415, the Department of Insurance shall allow as assets only such investments, cash and accounts, as are authorized by the existing laws of this state, or under the existing laws of the state or country under which such company is organized, and which investments it may approve or reject at the date of the investigation. In estimating the liabilities there shall be added, in addition to the capital stock, all outstanding claims, and a sum equal to the unearned premiums on the policies in force, calculated on the gross sum without any deductions on any account, charged to the policyholder on each respective risk from the date of the issuance of the policy. If the department finds this rule to be impracticable in ascertaining the condition of the certain kinds of insurance companies, it shall formulate such rules as it shall deem proper and efficient and consistent with law, having due regard to such rules as may be used in other states or approved by the National Association of Insurance Commissioners; Provided, in relation to the affairs of any foreign company, it may, in lieu of such examination and investigation, accept a certificate of the insurance commissioner or superintendent of such state or district as to its condition.