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 use strict;
use warnings;
...
Before suggesting code for that, I'd like to hear from the
OP whether this can really happen in "the real world" and
if such a solution is even needed.

# make the @$all array the union of everything in
# either @$all or @$accounts, excluding the acc 44443 record
...

my %seen;
@$all = grep{ $_->{acc} ne '44443' and !$seen{$_->{acc}}++ } @$all,@$a
+ccounts;

use strict;
use warnings;
...
  { acc => 54321, date => "1999-06-19", year => 2017 },
  { acc => 44443, date => "1980-03-05", year => 2019 },
]