When you built a selection with DESelect that doesn't give you the results you expect, check the following:
- Are the relations between data extensions / data views built correctly?
- Are the filters built correctly?
- When you write results to a target data extension that has a primary key, only the first record for a certain value of the primary key will be stored in the data extension. Any additional records for that primary key will be skipped. Make sure there are no primary keys set in the target data extension that could impact the results.