User Creation Template - Logon Name - Prevent Duplicate feature not working as needed

User Creation Template - Logon Name - Prevent Duplicate feature not working as needed

I'm working on trying to import a bulk batch of users via CS using the Bulk Import custom Creation Template.
As part of this I'm creating Logon names for these users.
AD doesn't don't allow for any duplicate logon names so I'm getting errors on some of my user creation attempts.

Our naming convention is a standard "lastname_firstinitial" so Tom Jones becomes "Jones_T" If there is already a Jones_T, Tom would then become Jones_To.
In order to achieve this naming convention I created a second naming convention that allows for this to work and set it to the logon name "Prevent Duplicate" portion of the logon name settings in the Creation Template.

However, so far it's not actually working and I'm still just getting errors about duplicate users existing.

Any tips or advice on what I'm missing here? Is there a better way?

                  New to ADSelfService Plus?