When data from GCal of the "User Provider" are imported overwrites data from previous user

I have to User Service Providers. Each user has its own "API Key", with its own "Service account email address" and his own "Calendar ID".

Each user, from Google Cal, modifies its own schedule to block their own availability in the calendar on-line.

When data from Google are imported into A +, manually or automatically, overwrites data from the previous user (?).

Never coexist data from both User Service Providers in the tab "Reserved by GCal".

Thanks in advance