Powerdrive from Rage Software/US Gold also uses level codes. I
keygenned the optimal codes for HOL to start on each level with maximum money and minimal damage.
From memory it used most of the alpha-numeric characters from the alphabet to represent values, so B might be 0, C might be 1, E might be 2 etc. Some keys were skipped (possibly to prevent O being typed as zero etc) and the name was also encoded that way. One of the characters was a checksum. The first block of characters was a value representing the damage for each part of the car in the game, hence why the codes all start with a string of B's then a C (for headlight damage).