OK, I nailed it. C<allow_loose_quotes> now also works inside quoted fields, under the condition that the C<escape_char> is not equal to the C<quote_char>. Code like that is very unlikely to have some valid escape sequence anyway. From 0.43 onward, you can parse those lines with

my $csv = Text::CSV_XS->new ({
    binary             => 1,
    allow_loose_quotes => 1,
    escape_char        => undef,
    });
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