There are obviously a few typo's. The outbound from Afrika to Europe should be NBO-LHR, no JNB-LHR, to get the right pricing.

Also I havent ticketed yet, but been in touch with BA in NBO and they said they had no issues with ticketing me when I'm passing through for work. Hope this clears the confusion.

Also, the route in it's last inception above passes the OW-validator on the bytestack site, so it has no issue with reentering Asia. As I read the rules on reentering, and attempted to put into the route, as long as the HKG-NRT-HKG is only a series of transits it should pass. The text on the issue:

"Any of these transit without stopover benefits can be taken in either direction (eg. Europe-SWP or SWP-Europe) and either before or after you wish to enter the continent for the second time to use your stopovers there. You can only leave and re-enter the continent of origin once, except for North America where you may have an additional transit without stopover."

I.e., I should be able to to the HKG-NRT-HKG, as long as it's a continous transit. Awkward, but fun.