I would say just get pictures of each head and look at them. I think I read somewhere to use the same part of your brain that you would recognize a face with. Don't look at specific details, like hair, nose, etc, just look to recognize them. Don't know if that helps
To me, the head of 93 looks a lot different, almost like she is a little chubby and younger. For the other two heads, another basic characteristic I look for is the distance from LIBERTY to the hair, on most of the head of 94's it's further away, on the head of 95s it closer.