Once a device is enrolled, it would drop into the "All Managed Clients" smart group.
If you want to group devices together that have been enrolled before/after a set date, you can use the "Last enrolment" criteria and choose one of the before/after/x number of days ago options, but if a device is wiped and re-enrolled, it would then also move into that smart group where it may have not been included prior to the wipe and re-enrolment activity.
You could possibly do some scripting/EA to scrape the creation date of a pre-stage admin account, or jamf binary installation (however that might update when a new version is installed), but again that would also update upon re-enrolment after a wipe event.
