https://userapps.support.sap.com/sap/support/knowledge/en/2731131
2731131 - IDoc with the ORDCHG message type is generated with only the changed segments from the PO...
After changing a purchase order (header and/or item level), an IDoc with the message type ORDCHG is generated. Although the IDoc contains only the segments...
https://userapps.support.sap.com/sap/support/knowledge/en/3439373
3439373 - ORDCHG Idoc is not Generated when Account Assignment is Changed Only in PO | SAP...
ORDCHG Idoc is not triggering for PO when only Account assignment fields are changed in ME22N. When performing only accounting changes from Ariba ORDCHG IDoc...