In an exceptional case, a court may enter a decree nunc pro tunc (now for then), with
an effective date sometime in the past. This action is not a retroactive decree as
such. Rather, it is properly an entry made now of something actually previously done
by the court to have effect from the previous date. It supplies not an omitted act,
but an omission in the record of an act which was taken but was not included in the
record through inadvertence or mistake. If a voidable marriage is properly annulled
by a decree nunc pro tunc, consider the effective date, rather than the date the decree
was entered, in determining when benefits become payable.