Hardly.... The 120 has never stood still. It is finalizing the 120-D testing as we speak and they are still working on improvements for later blocks.
ATK, the maker of the 120's motor, has recently been given a contract for a new motor. One of the planned upgrades is a "dual pulse" mode. This means that the motor can be restarted at the endgame to ensure full thrust, not just coasting, when it is near the target.
This, combined with the 120D's improved datalinks, will enable a very long range, high apogee, arching shot with full thrust at the end.