The paper A LOGICAL CALCULUS OF THE IDEAS IMMANENT IN NERVOUS ACTIVITY has the following description of neurons, which I question if there is errata or perhaps I need more information to understand this.

Looking at the picture below (b) is described as an OR gate. I’m confused because with either threshold being met on the $ N_1$ or $ N_2$ neuron, with thresholds 1 and 2, there are not enough inputs to reach the threshold of 3 for $ N_3$ . So how is this an OR gate?

(c) makes sense because the sum of the input to $ N_3$ is 3 when both $ N_1$ and $ N_2$ are at their thresholds.

Any guidance appreciated.