Solution : https://service.sap.com/sap/support/notes/151551 (SAP Service marketplace login required)
Key words : 
procedure detail screen 'person assignment', 'internally processed operation /external processing, detail screen 'person assignment', components pp-crp-sch, additional key words cn21, online service system            search, ps-dat-net component, alternative 'adjust basic dates', order start date lies, graphical capacity requirements planning
Related Notes : 
       
| 536487 | Composite SAP note on dates in the network | 
| 494487 | Project System: Consulting notes | 
| 207790 | Duration and dates in the PS Info System | 
| 156933 | Consulting: Scheduling routing | 
| 156115 | Consulting: Scheduling of planned order for recipe | 
| 152319 | Consulting: Scheduling of planned order for routing | 
| 151503 | Consulting: Scheduling of process order | 
| 150007 | Consulting: Scheduling of production orders |