Addition of Processor ID to Teensy Cards (and the web?) - perhaps on the back - for each processor declare these unique identifiers in some fashion for reference when coding or reading the sources.:

// Teensy-LC
#elif defined(__MKL26Z64__)
#define KINETISL

// Teensy 3.0
#if defined(__MK20DX128__)
#define KINETISK

// Teensy 3.1
#elif defined(__MK20DX256__)
#define KINETISK

and similar for future devices - as the processors in use grow this will be more important:
#elif defined(__MK64FX512__)
#elif defined(__MK66FX1M0__)