You seem to be encountering the rule I ran into last year. I was not allowed to upgrade a Europe-SouthAmerica because I went to far west first, then backtracked. I just wanted them to upgrade the Europe-DFW and DFW-South America portions skipping the DFW-XXX-DFW but was told two VIPs would be required because I was backtracking. (I was on a single fare basis with no stops over 24hrs).