I see quite a few drivers that can be a problem with a "go minded" attitude.
With all the folks on board, who had been contributing to the restoration, all were eager to fly, included the crew.
The limited time available before the actual ferry flight.
Possible the limited time the crew had (one was still on active duty with the airline) to complete the whole schedule, before needing to return the long way home.
And who knows what more.
That reflects in decisions like not returning to the hangar to investigate the stiffness of the rudder and the drifting during taxy. Especially from a test flight crew You might expect a critical attitude. Long time ago a very experienced colleague learned me that You can fly with nearly any problem, as long as You know the source and be able to make a risk assessment.
In all they had to operate in what I would call an 'hostile environment` with many distracting elements. Were this same flight to be flown at their home turf (including SL altitude and w/o pax), the outcome would have been different.
On the SA "validation" part: long time ago I used my (Dutch)ATPL as a basis to get a simple PPL (VFR) validation to use for renting a SE for sightseeing trips when I had a layover in JNB. I cannot describe the procedure other than terrible bureaucratic. It involved a trip to a field to do an early morning checkout and drive to Pretoria (office closed at 13.00hrs) with all the paperwork. My normal license which was valid for 2 Years, it included an IF rating with a due date always less that 6 months away, and the SA validation got limited to that date, no matter I said I did not want to include IF in my PPL. In practice every time I got there, I had to go over the same procedure every time, so after 3 times I gave up.
But maybe things have changed.
And for my flying abroad: I flew at many stops we had layovers: like in Alaska, LAX, Houston, Atlanta, NY, Chicago, Curacao, Nairobi, Santiago and even Thailand. Besides the XX thousands of airline hours have some 5500 hours on GA planes, but sometimes I just rented with a local instructor, to have someone O/B who knew all about local stuff. Having experience on a plane alone is not the whole story.