There's a note in the driver about that: "Explorer Chess and Chess Companion II / Concord have the same MCU ROM, pin P23 is either VCC or GND to distinguish between the two."

So, SciSys has put the 'sequel' to Travel Sensor and Companion on the same rom.
See the resemblence:
http://www.chesscomputeruk.com/html/...companion.html
http://www.chesscomputeruk.com/html/travel_sensor.html