Quality should be constant. There are many creative ways to achieve a higher level of completed evaluations.
Yada: Informal monitoring should done at least 50% of the day supported with immediate ad hoc coaching.
Formal evaluation don't necessarily have to be done by the Manager. Try giving your reps a blank form and ask them to evaluate themselves then defend why they scored it that way in a subsequent meeting with yourself. This method will enable you to boost the number of completed quality evaluations of your team.