There shall be maintained at all times by the exchange a reinsurance reserve in cash or securities authorized by the laws of the state in which the principal office of the attorney is located for the investment of similar funds of insurance companies doing the same kind of business, in an amount equal to fifty percent (50%) of the net annual premium deposits collected and credited to the accounts of subscribers on policies having one year or less to run and pro rata on those for longer periods or, in lieu of this amount, one hundred percent (100%) of the net unearned premium deposits collected and credited to the accounts of subscribers calculated separately for each policy in force as of any given date.