Solution : https://service.sap.com/sap/support/notes/438820 (SAP Service marketplace login required)
Key words : 
data inconsistency reason, /atg -> backup & restore, symptom inconsistent data, ale system group, ale recovery tool, time period system, inconsistent data, -time restore, ale recovery, data exchange
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| 605062 | FAQ: Restore and recovery | 
| 434647 | Point-in-time recovery in an SAP system group | 
| 434645 | Point-in-time recovery: What must I be aware of? |