Good Credit Cards Sometime Give Errors When No Card Type Specified

In this case, using iATS plugin 1.5.0

Our data entry contractor reported difficulties with some Visa credit card numbers.
After entering the number, the number and the security code produced error messages indicating that the card number and code were invalid.
The contractor did not enter the card type given that the card type field is supposedly optional

In Civi, I had her re-enter the card info actually setting the card type. Presto, It worked.

The short-term cure is obviously trivial – require the credit card type.

For extra points, make use of the front-end code that guesses the card type, i.e. backport the code in 4.7

I am not providing the card number for security reasons. But this issue is repeatable (I've gotten multiple complaints about it) and the obvious cure was not apparent to the data entry person. The cards are always accepted when entered directly into iATS's own website.