(b) Upon the basis of the report provided in subsection (a), including any supplements and amendments thereto, the Commonwealth Court may levy one or more assessments against all members of the insurer who are subject to assessment. No member shall be assessed for any loss that occurred when his policy was not in effect. No assessment shall be made or collection procedures begun after two years from the expiration date of a policy. The maximum assessment against any member for each year or part thereof in which a policy or policies issued to such member were in effect shall not exceed one hundred per centum of the average total annual premium during the life of the policy as written in such policy or policies including any increase or reduction in premium as the result of any endorsement thereto. Subject to any applicable legal limits on assessability, the aggregate assessment shall be for the amount that the sum of the probable liabilities, the expenses of administration and the estimated cost of collection of the assessment, exceeds the value of existing assets, with due regard being given to assessments that cannot be collected economically.