In cases like these I forego regexps for some kind of data language, such as Perl itself or JSON. I'd set up my defaults as a hash, then read a JSON object from a string (or a file, or wherever), then do a "hash slice" to override the defaults.

my %stuff =
(
  Title => 'some default',
  What => 'some default',
  'Date added' => 'some default',
  Data => 'some default'
);
use JSON;
my $newstuff = jsonToObj( <<STRING );
{
  "Title": "Gone With The Wind",
  "Date added": "January 16th, 2006 ( an optional source )"
}
STRING
@stuff{keys %$newstuff} = values %$newstuff;
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