Is that really the case? For example, while the following doesn't autovivify $h{A}{B}{C} it does autovivify $h{A}{B}.

use Data::Dumper;

my %h;

if ( exists( $h{A}{B}{C} ) ) {
    print "Hi mom!\n";
}

print Dumper \%h;
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$VAR1 = {
          'A' => {
                   'B' => {}
                 }
        };

use Data::Dumper;

my %h;
no autovivification;
if ( exists( $h{A}{B}{C} ) ) {
    print "Hi mom!\n";
}

print Dumper \%h;
__END__

$VAR1 = {};
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Ah! Here I was thinking that "no autovivification" was commentary.

    cpanp -i autovivification
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Runs script again... sweet.

Thank you kind Anonymous for enlightening this humble monk.