JayT, our horseradish was well established when we moved here, but I've dup up and given away some small pieces. My feeling is, that a small root will need a couple years to get well established. Maybe dig it up just to take a peek at it next year and if it looks good or has split into a couple taproots(like when a carrot splits into two roots) cut one of the tap roots off to use or cut a piece off the bottom just to sample, but put the large top and other taproot back into the ground. If it has split or started other roots, maybe take half, leave half.
Ain't nuthin like fresh horseradish, HUH!