First let me clarify some terms(from Selden Mast):
Mast Step is the hardware bolted on the boat to accept the mast.
Mast Heel is the fitting on the base of the mast that fits on the mast step.
From the information provided me I can say that on all boats the mast is connected to the mast foot by one bolt which bolts through a hole in the mast step and a corresponding hole in the mast heel. My guess is that they don't use two bolts in this configuration because it would stress the bolts as the mast pendulums. Some boats have this bolt in the center of the mast step and other boats have it on one side of the mast step. My boat has the bolt on the aft end of the mast step but other boats have the bolt on the forward end of the mast step. On the opposite end of where the bolt is located, there is another bolt, BUT this bolt fits in a slot in the mast step so the mast can pendulum without stressing the bolt. This bolt help keeps the mast in its place in the for and aft orientation. Below is drawing.