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 leading six digits of the card number is the issuer identification number (IIN), sometimes referred to as the bank identification number (BIN). The remaining numbers on the card are referred to as the primary account number or PAN. IINs and PANS have a certain level of internal structure and share a common numbering scheme set by ISO/IEC 7812.