Originally Posted by
thois
You should be able to pay the historical fare difference to upgrade from DONE3 to DONE4.
It could be possible that the ticket is purchased before the rule change, when the stop in Europe needed to be transit without stopover so that the computer doesn't allow to add Africa anymore. Even if that's the case, you might be able to get over it by referring to current rules.
Technically, if you are using historical fare, you can't refer to new rules that become effective after original purchase. In reality, what the airline will say, I don't know.