This does tweak Subst.pm slightly to allow it NOT to substitute
a given variable.

That way, we parse the finished product, subst EVERYTHING but the
variable we nee, AND ensure it matches precisely what we want.

Index: OpenBSD/PkgCreate.pm
===================================================================
RCS file: /vide/cvs/src/usr.sbin/pkg_add/OpenBSD/PkgCreate.pm,v
diff -u -p -r1.200 PkgCreate.pm
--- OpenBSD/PkgCreate.pm	15 Sep 2025 01:59:37 -0000	1.200
+++ OpenBSD/PkgCreate.pm	20 Nov 2025 14:15:55 -0000
@@ -771,11 +771,13 @@ sub check_version($self, $state, $unsubs
 {
 	my @l  = $self->parse($self->name);
 	if (defined $l[0]) {
-		if (!$unsubst =~ m/\$\{LIB$l[0]_VERSION\}/) {
-			$state->error(
-			    "Incorrectly versioned shared library: #1", 
-			    $unsubst);
+		my $k = "LIB$l[0]_VERSION";
+		my $r = $state->{subst}->do($unsubst, $k);
+		if ($r =~ m/\blib\Q$l[0]\E\.so\.\$\{$k\}$/) {
+			return;
 		}
+		$state->error("Incorrectly versioned shared library: #1", 
+		    $unsubst);
 	} else {
 		$state->error("Invalid shared library #1", $unsubst);
 	}
@@ -1205,7 +1207,7 @@ sub read_fragments($self, $state, $plist
 	# XXX some things, like @comment no checksum, don't produce an object
 				my $o = &$cont($s);
 				if (defined $o) {
-					$o->check_version($state, $s);
+					$o->check_version($state, $l);
 					$self->annotate($o, $l, $file);
 				}
 			}
Index: OpenBSD/Subst.pm
===================================================================
RCS file: /vide/cvs/src/usr.sbin/pkg_add/OpenBSD/Subst.pm,v
diff -u -p -r1.27 Subst.pm
--- OpenBSD/Subst.pm	27 May 2025 03:42:59 -0000	1.27
+++ OpenBSD/Subst.pm	20 Nov 2025 14:09:10 -0000
@@ -63,11 +63,14 @@ sub parse_option($self, $opt)
 	}
 }
 
-sub do($self, $s)
+sub do($self, $s, $without = undef)
 {
 	return $s unless $s =~ m/\$/o;	# no need to subst if no $
 	while ( my $k = ($s =~ m/\$\{([A-Za-z_][^\}]*)\}/o)[0] ) {
 		my $v = $self->{$k};
+		if (defined $without && $without eq $k) {
+			$v = undef;
+		}
 		unless ( defined $v ) { $v = "\$\\\{$k\}"; }
 		$s =~ s/\$\{\Q$k\E\}/$v/g;
 	}