Make sure the LEDs are fully open, it could be that at 20mA, the led is still partially closed, so you see a lower voltage. May be 8.5v..9v at 50-100mA.
A led can have multiple diodes in series internally, so you'd get only two terminals.
Besides opening one led to visually see the diodes, you could limit the current to a very low amount, like 1-5mA and use a microscope or some camera in macro mode to see each diode in the led light up (at a level that your eyes may not detect)