Problem resolved.
In “Customising - Archiving Object-Specific Customizing: Technical Settings”, found that the Production Mode Variant was defaulted to "Test Mode". After changing the Production Mode Variant back to “Production Mode”, the “Delete” function could then be changed to “Production Mode” for Sessions 46-48 (as below) after executing the “Session 48” again. The Production Orders could also be deleted & cannot be displayed in CO03.
Tks,
KH Fong