Mcculloch and Pitts Neurons: Is there errata in this article? 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.
In the article mentioned, the figures each have a threshold of 2 for each neuron.  Therefore there is no errata.