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 digit of your credit card number is the industry identifier. This tells you the industry of the credit card issuer. For example, airline industry cards begin with a 1 or a 2. Travel or entertainment cards, such as American Express and Diners Club cards, begin with a 3.