Identifying multipleDC trains on the same track?
It is easy to add a Magnetometer/Compass such as https://learn.adafruit.com/adafruit-hmc5883l-breakout-triple-axis-magnetometer-compass-sensor/overview

As a train travels its heading changes through each curve allowing you to keep track of its position.  If that doesn't work for you how about activate the magnetometer with a series of small and large magnets.  SSSS = point 1, SSSL = point 2, SSLS = point 3, etc