Thanks, thijsseh. To be honest, I'm not that interested in the upgrade for JNB-DXB - it's a shortish flight on a 777, so seems a bit of a waste of valuable miles if I can't get the onward upgrade. In the old days, the upgrade of the second leg would be quite a bit cheaper in miles than upgrading both sectors, but it seems that's changed and now upgrading only the DXB to JFK leg costs the same as upgrading both sectors - extremely irritating!
I do have an alert set for upgrade availability on the second leg (alert only, not auto-upgrade) - are these alerts reliable or should I keep checking manually?