I don't get either "Oh No!" comments.

Then $rec{NOTE} exists, but contains a value other than "Beware!".

But with Nested Hashes I still get the intermediate hash autovivified

The following contains a dereference:

$rec{NOTE}{Nested}
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You could have written it as follows:

$rec{NOTE}->{Nested}
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If you factor in autovivification, then the above is equivalent to the following:

( $rec{NOTE} //= {} )->{Nested}
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To get autovivified, $rec{NOTE} has to be undefined (or nonexistent), which is consistent with what we already knew (existent and not equal to "Beware!").

By the way, that means (1) would have given you a warning if you had warnings on as you should.

---

use strict;
use warnings;
no warnings 'void';

my %rec;

printf "exists:  %s\n", exists($rec{NOTE})  ?1:0; 
printf "defined: %s\n", defined($rec{NOTE}) ?1:0;
printf "true:    %s\n", $rec{NOTE}          ?1:0;
print "--\n";

$rec{NOTE} = undef;

printf "exists:  %s\n", exists($rec{NOTE})  ?1:0; 
printf "defined: %s\n", defined($rec{NOTE}) ?1:0;
printf "true:    %s\n", $rec{NOTE}          ?1:0;
print "--\n";

$rec{NOTE}{Nested};

printf "exists:  %s\n", exists($rec{NOTE})  ?1:0; 
printf "defined: %s\n", defined($rec{NOTE}) ?1:0;
printf "true:    %s\n", $rec{NOTE}          ?1:0;
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exists:  0
defined: 0
true:    0
--
exists:  1
defined: 0
true:    0
--
exists:  1
defined: 1
true:    1
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