Country 
South Africa
Province Free State Officially founded
1846 Elevation 1,395 m
(4,577 ft)
Specifically this was what I was refering to. There are 2 ways
to "calibrate" an altimeter (not sure of a freefaller uses the same
method). One uses local area air pressure taken at sea level. When
using this method, the user has to keep in mind the actual
elevation of the ground. Which in this case is about 4500+ feet.
This meant that the jumpers had only less than 8000 ft to reach the
ground. . The other method is to use air pressure taken on the
"hard deck", which is the ground. WIth this, the altimeter shows
the user his exact height off the ground, when on the ground his
altimeter should read 0. According to preliminary reports from the
news, the team broke off at 3500ft, making no reference to whether
they used the sea level or the ground elevation as the datum. If
both 12,500ft and 3500ft used in the report was based on ground
elevation, then the jumpers would have been exposed to an altitude
of 17,000ft. This is the height at which a normal person without
the aid of a breathing aparatus like 100% oxygen gets exposed to
hypoxia. What is not possible is that the report uses
the datum as sea level for both the altitudes reported, as
this would inevitably meant that the team broke off 1000ft below
the ground.
Regardless which method is being used, it is absolutely
essential that the correct pressure setting be input into the
altimeter. Errors can be big or small, and can be attributed to
erroneous input( due to a large number of human errors possible)
and changes to the air pressure with time, with the latter being
negligible most of the time. With sky diving sports, ground
elevation becomes more important as it gets higher, as factors such
as low air density, higher vertical velocity and unusual
readouts complicating an otherwise simple jump.