3737759 - MRP cannot generate planned orders starting in the past in SAP S/4HANA Cloud Public Edition

Although "Start in the Past" field is maintained in configuration activity 101173 - Define Scheduling Parameters for Planned Orders, MRP still cannot generate planned orders in the past.

SAP S/4HANA Cloud Public Edition

Although the "Start in Past" days is maintainedin configuration activity 101173 - Define Scheduling Parameters for Planned Orders, the MRP parameters at the plant level has a higher priority and will override this. At the plant level, by default, the "Start in Past" function is inactive and this cannot be changed in S/4HANA Cloud Public Edition system. As are result, MRP will never generate a planned order in the past. 

This is a limitation of  S/4HANA Cloud Public Edition system. 
There is already a feature request for this on the Customer Influence Portal:
Customer Influence request: enable planned orders in the past in public cloud

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