SCP itself is a sort of Telephone database that also provide services. Addition of new numbers is normally not done via SS7, infact a subscriber/number can only communicate and avail services of SCP via SS7. Number is created on SCP via its internal application interfaces and then subscriber can activate and use services via SS7.

There are few scenarios where number creation can be done via SS7 e.g. a small SCP providing voice mail service. A subscriber uses SS7 to contact SCP and on SS7 request, SCP adds the number to its database and creates an account for it.

But in particular SSP-STP-SCP scenario, creation is not done via SS7