@wjgregg it happened to me, I phoned DVLA and asked them why, a helpful woman looked into the application and explained to me that my Neurologist had ticked a box which made it sound like my MS was affecting my memory and concentration. If he hadn’t I would have got a 3 year one she explained.
I changed treating hospital in the meantime and explained to the next Neurologist what had happened. When the renewal came up for review I just made sure that they gave an accurate picture.
It was a pain but it was definitely worth the call to find out why only 1 year. It may even be just be an administrative error.