sampledTriSurfaceMesh reading surfaces from region directory

    IOobject
    (
        dict.lookup("surface"),
        mesh.time().constant(), // instance
        "triSurface",           // local
        mesh,                   // registry
        IOobject::MUST_READ,
        IOobject::NO_WRITE,
        false
    ),

So surfaces are taken from the mesh registry, which means regionName/constant/triSurface for etc. Could, however, have them taken from mesh.time() so that they use the main constant/triSurface

@Mattijs @Prashant

cross-reference EP#598