Can you use the trailing ,\d on the initial date/time to disambiguate? Consider:

use strict;
use warnings;

while (my $line = <DATA>) {
    my @parts = $line =~ /(\d{4}-\d{2}-\d{2})(?:,\s|$)/g;
    
    print $line;
    print "   ", join ("\n   ", @parts), "\n";
}


__DATA__
2009-02-02 06:12:57,500 dates processed: 2009-01-31, 2009-01-29, 2009-
+01-30
2009-02-18 06:03:47,713 dates processed: 2009-02-16, 2009-02-17
2009-02-19 05:58:29,138 dates processed: 2009-02-18
[download]

Prints:

2009-02-02 06:12:57,500 dates processed: 2009-01-31, 2009-01-29, 2009-
+01-30
   2009-01-31
   2009-01-29
   2009-01-30
2009-02-18 06:03:47,713 dates processed: 2009-02-16, 2009-02-17
   2009-02-16
   2009-02-17
2009-02-19 05:58:29,138 dates processed: 2009-02-18
   2009-02-18
[download]