What would be more correct is a CE dated after your car's date, especially if you had warranty paper work.
What it seems like thought is that most people prefer a correctly coded and closely dated engine ( a few weeks before assembly).
If it is a X22 nov 68 built car then the Dec 68 CE could have been installed if the motor was bad early in the vehicle's life. If it is a X22 Nov 69 car then it is one of the last X22's built and would have had an engine dated in Oct or a CE dated post vehicle assembly.