A. Blind spot
A. Blind spot
B. Dark spot
C. Hidden spot
If a truck has blind spot mirrors of blind spot monitors installed then it will have minimal blind spots to the side, but if you are right behind the truck then you could be totally invisible to the driver, especially if you've approached quickly from behind. You also can't expect a driver to be constantly looking in the mirror.
As you can see from this video, the mirrors installed in this truck give good visibility down the off-side. However, not all trucks have these mirrors - some don't have the one angled down at the front or side, or the convex one on the side.
This American video is useful if you reverse the sides of the blind spots (the driver will be sitting on the other side of the cab)
If you're looking at other videos online bear in mind there's a rubbish video showing a lot of cyclists in a blind spot. The truck's mirror is extremely poorly positioned.