Using small-angle neutron scattering (SANS) results, pressure-volume-temperature (PVT) data from both polymer melts and blends, and experimentally determined critical temperatures, we employ the lattice Born-Green-Yvon (BGY) theory in the development of new routes for the characterization of polymer fluids and polymer blends. In particular, we focus on blends of polystyrene (PS) with poly(vinyl methyl ether) (PVME) and tetramethylbisphenol A polycarbonate (TMPC). In the first part of the paper we use the analytic expressions derived from the lattice BGY theory to fit the experimental data via three separate routes, using the different kinds of experimental data. In the second part of the paper we investigated the extent to which each of the methods lead to a thermodynamically consistent picture of the blend. Among other findings, we conclude that it is possible to use a relatively sparse data set and still produce a quantitative description of both pure component and blend behavior.