Quote (John Baker):

There is no downward compatiblity in most any CAD system including UGS NX.  If you wish to preserve as much of the model drawing content as possible, you will need to use something like STEP or IGES to move newer files back to an older format.  The Parasolid export route is recommended for moving surface and solid models where there is a need for an exact (non-conversion) representation, such as moving a design model from a newer version to a older system for manufacturing.  However, only the surface and solid model can be moved in this manner.