Apple allows you to enroll devices that were purchased prior to your certification in the Apple Device Enrollment program. Devices that were purchased as far back as 2011 can be enrolled in the Apple Device Enrollment Program.
The best method is to create a product in your System of Record (Point of Sale or ERP) called: Apple Historical Device. You can set the cost and price at $0. Receive the serial numbers into your System of Record and create a sale to a customer with the correct Organizational ID (formerly DEP Customer ID).
It is also recommended to assign this product to a Supplier/Vendor = Apple and a Brand/Family = Apple if possible in your System of Record.
Sync this sales to Hyperspace and enroll them to the Apple Device Enrollment Program like any other sale.
IMPORTANT: It is very important that you verify that own all of the devices. If the devices were purchased a couple years ago it is very possible that one of the following has occurred to one or more devices.
A. The device was sent back for repair.
B. The device has been stolen or misplaced.
C. The device has been resold to a student.
It is your responsibility to verify that you own all the devices. Typically Apple recommends that you do a physical verification by examining the serial numbers on the back of each device. Enrolling invalid devices to the Apple Device Enrollment program can result in a suspension of your Apple Device Enrollment certification.