In support of the crew, to get a validation in SA, was (and is?) extremely bureaucratic and cumbersome, at least that was it 15 Yrs ago.
I did it a few times to get my SAA PPL, to rent a Cessna whenever I had a layover.
One of the irritating and stubborn views of the office was that the expiry date of part of my ATPL's IF rating was of course sooner than the ATPL itself.
They insisted that that date was then also the expiry date of my validation, even while it was a VFR PPL validation only! So with some luck I had it valid for 3-4 months.
After doing that a few times (my next trip was always after the expiry date...) I got fed up and never rented again.
Bureaucracy at its worst, thinking in hurdles in stead of possibilities.
Of course the government tries to "protect" the local pilots of not giving away an ATPL too easily, but they could have stated on it, that is was only for a few test flights on that specific plane plus the outward bound.
Try that with a driver's license of a foreign visitor and the local rental car businesses would be crying out...
The report does not state why the crew did not/could not obtain a suitable validation, I am sure they tried!. If this was because of a missing check flight, I swallow my words, but they might not have gotten even close to this point. Instead the report mentions the missing licensing several times. But no word WHY it was missing...