Time Zone File format - When does tzh_ttisgmtcnt or tzh_ttisstdcnt differ from tzh_typecnt, and how, and why?

[Jonathan Leffler]

In tzfile.5.txt, it says:

tzh_ttisgmtcnt
    The number of UTC/local indicators stored in the file.

tzh_ttisstdcnt
   The number of standard/wall indicators stored in the file.
...
tzh_typecnt
    The number of "local time types" for which data is stored in the file
(must not be zero).

Empirically, in the tzdata2007h and tzdataj data sets, the values of
tzh_ttisgmtcnt, tzh_ttisstdcnt and tzh_typecnt are always identical.

Under what circumstances are there any differences in the three values?

If the answer is "when the stdcnt or gmtcnt is zero", when does that happen?
If the answer is "when the stdcnt or gmtcnt is a non-zero value different
from typecnt", then what do the values mean?

If the answer is "there isn't any difference any more, but historically,
there was a transition period when they weren't all present and the stdcnt
and gmtcnt were sometimes zero back then", then I can live with that as a
satisfactory enough explanation.

-- 
Jonathan Leffler <jonathan.leffler at gmail.com>  #include <disclaimer.h>
Guardian of DBD::Informix - v2007.0914 - http://dbi.perl.org
"Blessed are we who can laugh at ourselves, for we shall never cease to be
amused."
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