Based on initial findings by Jimmy there were items that were tagged as Parent SKU in SETDTL table but were not set code in INVMST is not M. 
Steps:
1. Query all items tagged as Parent SKU in SETDTL but set code in INVMST is zero and isetqt in SETDTL is not equal to zero
2. Update all SKUs(420 records) in INVMST and change set code of these items to 'M'
3.  Validate if update is correct using Option 03 - Inventory sets under MENTB5
