It's still today's date, but improving on that seems non-trivial.
# from the local build environment when building distribution packages.
LC_TIME=C; export LC_TIME
unset LANG
# from the local build environment when building distribution packages.
LC_TIME=C; export LC_TIME
unset LANG
-datestamp=`date '+%B %d, %Y'`
+datestamp=`date +%Y-%m-%d`
cat <<__HOOPY_FROOD
.TH MH-CHART %manext7% "${datestamp}" "%nmhversion%"
cat <<__HOOPY_FROOD
.TH MH-CHART %manext7% "${datestamp}" "%nmhversion%"