If you want to get accurate deployment success rate(%), it's required to manage obsolete client on daily basis.
What I do normally:
Open SMS Administrator Console-> Expand Site Hierarchy-> Expand Site Settings->Expand Site Manitenance-> Select tasks-> open "Delete obsolete Client Discovery data" properties and enable it.
You need to delete data older than 1 days.
After that click on the "All Systems" collection and check whether any client still shows as obsolete. You can delete those client from the console itself.
Note: During the deployment, package can be targeted to non obsolete clients only.