There are two factors to consider when deciding how to handle the problem of a work sample: sample size and population characteristics. Sample size is determined by a formula based on the power of the sample or its ability to represent the population with a predictable margin of error.
The resulting complexity makes card type detection code difficult to write, read, and maintain. As an example of this complexity, consider this JavaScript regular expression used to detect Discover card numbers starting with 6011, 622126-622925, 644-649, and 65:
Credit card numbers are ISO 7812 numbers. As an ISO 7812 number it contains: 1  A single-digit major industry identifier (MII) (the MII is considered to be part of the issuer identifier number), a six-digit issuer identifier number (IIN), an account number, and a single digit checksum using the Luhn algorithm.