There is no longer a need to use the percent = zero on an enrollment record to exclude that enrollment record from being extracted. Instead use the Exclude from State Reporting check box that you will find next to the Leave Code on the MARSS tab of the Student view.
In fact, if you do you will see an error in the MARSS extract log where the message will say Invalid Data type for field.
The MARSS B – Report of Missing State Numbers will have commas with no student names in the report.
If you have any of these, you can easily find your students with a simple query of the percent of enrollment field (EnrUserNum1), and sort the report by that field in ascending order. You can do this focused at a given school or at the district level (recommended).