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 "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.