Yes, tracks will get overwritten depending on the unit and the available memory. It’s best to put most of your stuff on an SD card if you have an expansion slot, and that will free up the internal memory. You might also be able to change the time interval in which the points are recorded (x/minute, etc).
Most units have the option to save/convert the logs to actual tracks. You can do that after each day of riding and you won’t loose anything even if it does start to overwrite the track logs.