seems to me that you expect that the method verify() will only check the last digit, but the author expect a more usefull check for "real life".

Note: having $code, you can chop it and generate the last digit, then compare with the chopped one.

Oha

Update: i do not agree to suggest to fork the module, probably you can ask the author to make a verify_last_digit() method which does not check the length?