(a) Notwithstanding any other provision of this subpart, except as provided in paragraph (b) of this section, a Certificate of Documentation but no trade endorsement thereon, issued to a vessel which is the subject of an outstanding mortgage filed or recorded in accordance with subpart Q of this part or any predecessor regulations, remains valid for purposes of:

(1) 46 U.S.C. chapter 125;

(2) 46 U.S.C. chapter 313 for an instrument filed or recorded before the date of invalidation, and an assignment or a notice of claim of lien filed after that date;

(3) 46 U.S.C. 56101,56102; and

(4) 46 U.S.C. 56301.

(b) The provisions of paragraph (a) of this section do not apply to a vessel which is subject only to a mortgage filed or recorded before January 1, 1989, which had not attained preferred status as of that date.