Hi,
According to me, the process is such that firstly all the expenses are booked in an Internal Order, then the same are settled periodically or fully on an AUC by executing KO88. Now the values is transferred from Internal Order to AUC. Now Settlement of AUC Asset is done by executing AIAB and AIBU, by this the value flows from the AUC Asset to the Final Asset.
But you can also transfer the valeus from AUC Asset to FInal Asset usign T-Code ABUMN. But in Asset Explorer both the things are shown differently.
Regards,
Malhar.