It is unlikely that the horse you were riding was a Hanoverian, or at least registered as one. All Hanoverians with brands have them on their left hind thigh, it is two horse heads in the shape of an “H”. The only breeds I know of that have brands on their necks are mustangs or some Arabs, was it a freeze brand, like white markings? Also, all Hanoverians are named in the registry with a name starting with the same letter as their sire, so for instance, Hanoverians sired by Donnerhall would all have names starting with a “D”. If your horse was registered as a Hanoverian under the name Coby, then his sire would be a “C” line. If your horse were a mare, I would say it was possible that she was accepted in the Hanoverian studbook but was another breed, such as an Arabian, but it sounds like it was a male, so that wouldn’t be the case. But from your info, it sounds like your horse was probably another breed. If it was a nice moving, quality horse I would say probably an Arab or some kind of cross bred, and I’m not sure how to read those brands. The Hanoverian brand looks something like “)(” on the left hind thigh. Hope this helps!