Looking at newer automake I noticed the autoconf version should have been bumped with the 1.16.4 release.
Index: Makefile =================================================================== RCS file: /cvs/ports/devel/automake/1.16/Makefile,v retrieving revision 1.9 diff -u -p -u -p -r1.9 Makefile --- Makefile 9 Sep 2023 12:35:16 -0000 1.9 +++ Makefile 28 Nov 2024 05:38:10 -0000 @@ -1,10 +1,11 @@ VERSION= 1.16 DISTNAME= automake-${VERSION}.5 +REVISION= 0 PKGSPEC= automake->=${VERSION},<1.17 EXTRACT_SUFX= .tar.xz PORTROACH = -AUTOCONF_VERSION= 2.69 +AUTOCONF_VERSION= 2.71 post-install: cd ${PREFIX}/info && mv automake.info automake${SUFFIX}.info