(a) If articles of incorporation limit indemnification or advance for expenses, indemnification and advance for expenses are valid only to the extent consistent with the articles.
(b) This Part does not limit a corporation's power to pay or reimburse expenses incurred by a director in connection with his appearance as a witness in a proceeding at a time when he has not been made a named defendant or respondent to the proceeding.
(c) This Part shall not affect rights or liabilities arising out of acts or omissions occurring before October 1, 1990.