There seems to be some mistake here. Any careful reader of the Contra Gentiles will find in (e.g., Chapp. LXI, 1: LXXVI, note) indications of the want of the author's final revision, a task much more difficult with a manuscript than with a printed work. Every modern author finds sundry small corrections necessary as he is going through the press. The fact that the objection is based upon the self-same principle which St Thomas invokes in his reply to it, namely that neither in nothingness nor in the eternity of God can there be assigned any difference of instants. From this admitted principle the opponent argues that God must have created from all eternity. St Thomas in reply allows that eternity affords us no means of fixing the date of creation: still, he contends, we have a measure of the date in the time that has elapsed since, which, even though we do not know it, is a knowable finite quantity.
Of God and His Creatures: 2.32