I didn’t read for comprehension but noticed this–

–upon which you remarked, so far so good. It’s wrong of course. It should read TÓIBÍN and would if your strings were properly decoded prior to the uc operation. So regardless of anything else that’s going wrong, the population of your $data is broken.

use warnings;
use strict;
use Encode;
use open qw( :std :utf8 );

my $start = "Colm Tóibín";
print decode("UTF-8", uc $start), $/;
print uc decode("UTF-8", $start), $/;

__END__
COLM TóIBíN
COLM TÓIBÍN
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