I found it interesting the other day when I was looking at my single edge (SE) razors.
The older Gem, 1912 loads the blade by placing the blade in edge first. The front of the blade actually hooks into two small hooks near the comb of the razor. The back of the blade then falls into the body of the razor. THe lid then snaps down over the blade and holds everything securely in place.
The newer Gem loads the blades by placing the blade into the razor back first. There is a small post in the center that corresponds to a hole in the center of the razor. The lid then closes down on the blade to hold the blade in place. There are also small tabs that correspond to the edge notches helping to further align things.
By the way, these shave great.