Mahendra,
As push deployment would trigger STO which eventually will go to ECC. In this case you need to write logic while CIFing STO from APO to ECC that it checks for material documents which ware posted latest and have not been mapped in any STO (need to do mapping in ECC also). This could be done through EXIT_SAPLMEPI_006 and populate this is in custom field in ECC in STO itself. Finally copy the same from STO to APO with above exit (EXIT_/SAPAPO/SAPLCIF_PU_001) to APO.
This will make sure that you can track both in ECC & APO and can find unassigned document easily.
Regards
Rahul