I haven't looked at the code, but testing indicates the following are probably true:

1) %g and %G do not seems to be recognized as year formats; only %y and %Y seem to work. I think %g and %G are meant to be used in conjunction with ISO 8601 week numbers (e.g. %V).

2) adding a space helps a lot - otherwise only a single year digit works:

$date = "05Jul 08"; # work with pattern => "%d%b %y"
$date = "05Jul8"; # works with pattern => "%d%b%y"
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