Consider the following rxnsreactions:
$$\begin{align}\ce{C + O2&->CO2}\tag{1}\\[1em] \ce{2C + O2&->2CO}\tag{2}\\[1em] \ce{2CO + O2&->2CO2}\tag{3}\\[1.5em] [(2)+(3)]/2 &= (1)\end{align}$$
Since $G$ is a state function, why aren't the straight lines corresponding to these reactions in the Ellingham diagram concurrent?
I have checked the graph from other sites but found none to be concurrent. Is there some kind of error in data or extrapolation of the graphs or any other specific reason for this?