If you have 2 seperate number plate lamp assemblys each with 1 bulb per assembly and a bulb is not working in one of them then it is a fail

But (there are always buts in MOT) if you have one number plate lamp assembly (with no divider between internal reflector or the bulbs) with 2 x bulbs and one bulb is not working then it is a pass and advise

There is a new test criteria just been added that requires 50% of the light source to be working

This was mainly bought in to cover multi LED powered lamps but is relevant to bulbs as well

So if you have for example 6 leds in 1 single number plate assembly then 3 working LED's is a pass and advise

Hope this helps