Typically the guidance seen is that on LEDs the long pin is the anode and the short pin is the cathode. Often it's also said that if you look inside the LED, the large plate is the cathode while the small plate is the anode.
However, this Lite-On LED has the anode on the short pin according to the datasheet. The short pin is still connected to the large plate, however.
I've confirmed that you must wire the short pin to the positive terminal of the battery for the LED to light up. What gives? First of all, is there a reason the convention is broken? Also, how come the plates are also seemingly reversed? Is there any particular reason for this or is it just manufacturer discretion?