Credit Card plugin error handling messages

The error handling messages for the Credit Card plugin are somewhat confusing. For example, entering the incorrect card number returns Number failed checksum test - not very helpful to customers. Has anyone done any testing to create more meaningful error messages? If so, would you be so kind as to share so we don't waste a lot of time testing? Here's the default list we have so far:

$CCVSErrNumberString = 'Number isn\'t a string';
$CCVSErrVisa14 = 'Visa usually has 16 or 13 digits, but you entered 14';
$CCVSErrUnknown = 'First four digits, %s, indicate unknown card type';
$CCVSErrAccepted = 'Programmer improperly used the Accepted argument';
$CCVSErrNoAccept = 'We don\'t accept %s cards';
$CCVSErrShort = 'Number is missing %s digit(s)';
$CCVSErrLong = 'Number has %s too many digit(s)';
$CCVSErrChecksum = 'Number failed checksum test';
$CCVSErrMonthString = 'Month isn\'t a string';
$CCVSErrMonthFormat = 'Month has invalid format';
$CCVSErrYearString = 'Year isn\'t a string';
$CCVSErrYearFormat = 'Year has invalid format';
$CCVSErrExpired = 'Card has expired';
Thanks.