Ok I tracked this issue down to an SEO mod. The previous developer had installed both Simple SEO and Ultimate SEO, and it appeared the store was upgraded to 1.5 from 1.3 as the mods were half installed. Some mods had the files or added code in the Zencart fileset and entries in the DB, but weren't showing in Admin. It's been a mess. The only issue I have now is the site categories are redirecting from localhost to the live server. I think I may be better off with a fresh install, then re-importing products/categories.