Custom process for SKU assignment: GappaSku Updates ?

Hi,

In 9.1, neither inheritance or categories cover our needs for Google Workspace SKU handling and assignment. Therefore we're working on our own customized process for stock calculation and license type handling for workspace accounts. 

We've noticed that whenever a new license is assigned to a Workspace account, there's only one process  (an update) and projection for the GappaSku table. But in fact, an insert is performed in GappUserInPaSku too.We dont get to know how a simple update in GappaSku gets the assigned account and perform the insert in the userinsku table. But understanding this behavior is vital when it comes to design our custom processes and scripts.

Any hints?

Thanks!!