Have there been any errors during SOLR tracking (check solr.log / alfresco.log and provide here for reference)? Can you check via the NodeBrowser if any of the other sites have the aspects cm:indexControl or sys:hidden applied?
Note that the SITE field will only show values for any site if that site has at least a few indexed items. Any empty site (without any initialised site containers like documentLibrary) will not show up at all.
It would be nice of you if you could explain your problem and solution here for other people who may be interested or even have the same issue (even if it turns out it was just a configuration mistake).