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:
The first 6 digits of a credit card number are known as the Issuer Identification Number (IIN), previously known as bank identification number (BIN). These identify the institution that issued the card to the card holder. 400115 - Visa Electron Barclays. 400121 - Electron IRL.