When the first change notice is close to completion you don't want a second one fouling up the works (at least for the humans). For example if the first change notice has all the implementation tasks completed and the review and audit tasks are all that are left, we consider it too late to go back and add more changes in. Much less confusing to complete it and then work on a second one.
Earlier in the process you are correct, it is better to incorporate one or more change requests into a single change notice.
The situation that led to this question is an individual that ignored the change flag icon and wrote a second set of change request and notices. The affected data on the second was the same version as the first. However when the first change notice was completed, the second change notice should have had the latest version in affected data and did not.