Yes, well, uncooked and/or those you've stashed, cooked, from other meals. 'Cooked' in this case could mean other bones from other smoking sessions, grilling sessions, roasting. Depending on what the point if the stock will be, it can be good to use cooked and uncooked, and can be good if some meat is left on them. Pork neck bones are good additions (and are often cheap).