Recent Density Functional Theory and simulation studies of wetting and drying transitions in systems with long-ranged, dispersion-like forces, away from the near vicinity of the bulk critical temperature Tc, have questioned the generality of the global surface phase diagrams for wetting, due to Nakanishi and Fisher, pertinent to systems with short-ranged forces. We extend these studies deriving fully analytic results which determine the surface phase diagrams over the whole temperature range up to Tc. The phase boundaries, order of, and asymmetry between, the lines of wetting and drying transitions are determined exactly showing that they always converge to an ordinary surface critical point. We highlight the importance of lines of maximally multicritical wetting and drying transitions, for which we determine the exact critical singularities.