(a) A national bank's investment in securities that no longer conform to this part but conformed when made will not be deemed in violation but instead will be treated as nonconforming if the reason why the investment no longer conforms to this part is because:
(1) The bank's capital declines;
(2) Issuers, obligors, or credit-enhancers merge;
(3) Issuers become related directly or indirectly through common control;
(4) The investment securities rules change;
(5) The security no longer qualifies as an investment security; or
(6) Other events identified by the OCC occur.
(b) A bank shall exercise reasonable efforts to bring an investment that is nonconforming as a result of events described in paragraph (a) of this section into conformity with this part unless to do so would be inconsistent with safe and sound banking practices.