So - this is a guess, but have a look at this -- How to enable the Inventory option Store Scans on the Core Management Console -- and (re-)run the process for your NUC (what's a NUC btw?) device to TRY and boot into provisioning.
The part you're going to be interested in is the mini scanfile that'll be generated when the device boots & sends it to the Core (this is essentially the part where we "try to marry on MAC address / Serial ##" based on the data in the scan file).
Questions essentially amount to:
- *DOES* the Serial number actually show up in the scan file ANYWHERE in the first place ? (I'll explain why I'm asking this in a second).
- Does the Serial number show up in the RIGHT place ...? And/or is it the string you expect it to be (a *LOT* of hardware vendors tend to either put serial numbers into "interesting" locations, and/or tend to have them along side other stuff, so instead of a "My-Serial-Number" string, you may get a "My-Serial-Number-010101" type string.
- Based on the above, you can potentially re-work your Provisioning process & create your "base" inventory records via script / hand, and fix them up (an inventory scan file is JUST a text file, so you can edit those quite happily ... and if you want/need them processed, just copy them into the LDSCAN folder, where the inventory service will hoover them up).
... that should give you a basic starting point to work from, hopefully.