:Henley says "The nomenclature is far from standardized, and...no standardization can be expected in the foreseeable future." He uses 'flow graph' and 'signal flow graph' interchangeably (more often 'flow graph' as it is more compact, I guess) and defines the 'flow graph' like this:(p. 2) 
 ::"Flow graphs are a graphic representation of sets of linear algebraic or linear differential equations. Each vertex of a graph represents a variable of the equation...The coefficients aij written alongside the branches are referred to as gains, branch gains or transmittances. They are the operators that map node xi into node xj, i.e. xi=aijxj. The term transfer function is frequently used if xi, xj are functions of the Laplace operator s." 

 Evidently, Henley's 'flow graph' is not restricted to either the Mason or the Coates graph, but includes both.