Is it possible for Non-DEP Devices to be registered through a certified reseller after the fact ?

Typically it will have to be the reseller which they were purchased though, and we have had good luck getting our resellers to do exactly this.

It’s just possible if the devices were bought through a DEP Reseller and for models later than 2012.

Fortunately Apple announced a way to do this manually a few weeks ago at the WWDC.
Maybe you would like to have a look into this 10min video:

https://developer.apple.com/wwdc21/10297

Unfortunately the process needs devices running a T2 or Apple Silicon Chip and macOS Monterey. But it should definitely help for future purchases.

Best,
D.

Thank you for the answers. Its unfortunate that Apple Configurator will only be usable on new macOS devices but a interesting thing to keep in mind for the future.

As for the Apple School manager topic, in another thread PaulHazelden said this :

"It is possible for Apple to do it for you. They have an internal order number system, and they need to find those numbers. If you give the serial numbers for the Macs to your Apple Rep, you should be able to get them to find the Initial Apple Purchase order number. Then you should be able to press them to add them to your ASM. They really do not like doing it. The Order number thing is the key, get that for each and then move on to get them added. In theory any, really nice kind helpful, reseller can add them with the order number details.
If you look in your ASM and existing assignments you should see the Apple order numbers for their entry."

Does anyone have experience with this progress ?

Other then that i found a different thread that had some interesting information about a DEP like experience on Non-Dep Devices that linked me to this presentation. I havent had the time to complete watching it yet though but what i saw was pretty interesting.

https://www.youtube.com/watch?v=RYgsEx2YR3c

As I said, it is possible.
A device was purchased through a supermarket, (because it was cheap)
After a lot of questions to one of our main suppliers, I found out about the Apple Purchase order numbers. Then I managed to get our Apple rep to find the right one for the device. And finally I got it added to DEP. Took ages (read months), and Apple threw up walls and walls at me. Passed me from one department to another - emails and phone calls. But eventually it was done. This was some years back though. Since then ALL purchases have to be made through our approved resellers.
You just have to keep going and don't take no as an answer. You will have to prove ownership to them. I had a receipt for it.
Maybe someone at Apple got told off for doing it, I don't know. But it was done.