A platform cooling arrangement for a turbine rotor blade having a platform and an interior cooling passage and, in operation, a high-pressure coolant region and a low-pressure coolant region, wherein the platform includes a topside, which extends from the airfoil to a pressure side slashface, and an underside. The platform cooling arrangement may include: an airfoil manifold that resides near the junction of the pressure face of the airfoil and the platform; a slashface manifold that resides near the pressure side slashface; a high-pressure connector that connects the airfoil manifold to a high-pressure coolant region of the interior cooling passage; a low-pressure connector that connects the slashface manifold to a low-pressure coolant region of the interior cooling passage; cooling apertures that extend from a starting point along the pressure side slashface to a connection with the airfoil manifold, bisecting the slashface manifold therebetween; and a plurality of non-integral plugs.