A bare "%s" in a zone line such as ...
Zone Africa/Windhoek 2:00 Namibia %s
...means that the abbreviations are completely specified in the Rule lines being used. In this case, the operative Rule lines are...
Rule Namibia 1994 only - Mar 21 0:00 -1:00 WAT
Rule Namibia 1994 2017 - Sep Sun>=1 2:00 0 CAT
Rule Namibia 1995 2017 - Apr Sun>=1 2:00 -1:00 WAT
...and so the abbreviations "WAT" and "CAT" are the result.
@dashdashado