To determine the potential of a producing formation, theoperator...

To determine the potential of a producing formation, the
operator may order a drill stem test (DST). The DST crew
makes up the test tool on the bottom of the drill stem, then
lowers it to the bottom of the hole. Weight is applied to the
tool to expand a hard rubber sealer called a packer. Opening
the tool ports allows the formation pressure to be tested.
This process enables workers to determine whether the well
can be produced.

Hence you can see that a drill stem test only provides a sample of the fluids in the well and the Mirage 4 DST was successful.

Cheers.......MT.