I’ve got copies of the artillery rolls for the Crimea Medal but haven’t managed to locate his entry, but its clear that W = “wounded date unknown” and WO = “wounded on” and is usually but not always accompanied with a date as d/m/y or d/m.

He doesn’t appear in the official casualty lists at http://www.britishmedals.us/kevin/casualty.html but they are known to be incomplete and exclude sickness. Many of those wounded became ill some died in the Crimea, but others were shipped home, in which case you’ll need to check Civil death index.

Jeff