The customer implemented the SG Connector for SCCM for their instance. It is correctly importing all installation information. It is not correctly creating software installations on the machines.
The below business rule controls the entry of s/w records in cmdb_sam_sw_install table.
'Remove Installs For Retired/Stolen CI'
If this rule is active, it will delete entry in cmdb_sam_sw_install if the computer is not operational.
This is an expected behavior. However, if you want to add software installs for the retired computers as well, you can deactivate the business rule or change the status of the computers to operational.