Re: What is the latest Summer 16 Org version number?
16.50.016 was the GA release for Summer 16 (released on 9/13/16). I believe you saw reference to this in the Fixed Issues List you mentioned. There may be interim builds after that but some of these are done for specific customers for specific issues and not necessarily something available for all. I'm not sure why you have an earlier build in sandbox. Did you perhaps start testing prior to the official release? That may be where the discrepancy is.