Lenses 1 and 3 are long nose, 2 and 4 are pancakes.
Look at how much barrel there is between the silver ring and the top of the lens. Or, if you like this perspective better, look at the front element - in lenses 1 and 3 it is deeply recessed while in 2 and 4 it lies almost flat with the filter ring.

In absolute terms the difference is not remarkable. It's a 50mm lens after all. If you held them in your hands the difference would be obvious.