References quick reference might be helpful in figuring out how to get ideas down into code.

A concrete idea is that your long list of hashes should all be one hash of hashes. That reduces the insert lines down to something like:

my $base = substr($grp, 0, 3);
if (exists $is_hierarchy{$base}) {
  $dsc{$base}{$grp} = $dsc;
  $title = "$base$ng";
}
else {
  $dsc{other}{$grp} = $dsc;
}
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(And then the information about all of the different hierarchies you have has to be popualted in a hash %is_hierarchy.)