You can validate your enrollments by verifying the instructional design, leverage reports and tools like the Check UIC feature to verify entries and ultimately ensure that your data is accurate.
The validation tools will illuminate errors in case of invalid data (data not meeting specified requirements and criteria). However, if the basic data entered is incorrect, like a student was entered into a wrong course or the student was not assigned the correct segments, then such mistakes will not generate any errors. Thus, you may not get the completers that you hoped for. So, to prevent issues like these that may arise due to wrongly entered data you are required to check your instructional design and use the reports available to you to determine any such data discrepancies. Accurate data will project completers correctly.
For detailed steps on how to validate your enrollments refer to The Enrollment and Completion Collection Guide.