True!!
The main difference between tasks at header level [QMFE-FENUM => Blank] and Item Level [QMFE-FENUM ≠ Blank, e.g; "1" ] and similarly activities at header level [QMMA-FENUM = Blank] and item level [QMMA-FENUM ≠ Blank, e.g; "1"]. Also the sort number [QMMA-QMANUM] will suggest in which order the Activities are created and Activity text [QMMA-MATXT] can be used to save the reference of the Item task, against which this is created.
If One task creates more than one Activities then the reference short text can be used to capture this assignment. Else, technically there can't be any linkage between Tasks and Activities, be it at header level or Item level, as both accesses different catalog types.
But still I have a basic question - what & how is the differentiation possible between Corrective Actions and Preventive actions. And as I proposed, Follow-up actions can be an option to explore the feasibility of any such requirement, where any task is creating any linked activity.