SM-2 vs SM-3 ?
It's a slight misnomer to Refer to the SM-2 Block III as an Older Version of the SM-3, As I understand it the SM-3 is pretty much a dedicated Anti-Ballistic Missile weapon whereas SM-2 is primaily an Anti-Cruise-Missile and Anti-Aircraft weapon (with a secondary ability to be used on surface ships as far as the horizon) with no signifcant Anti Ballistic Missile role and little in common between the two, except that they are fired from the same multipurpose Vertical Launcher that launches almost all the US Navy's current surface lanched missiles, including Tomahawks and Anti Submarine Missiles.
Why are they desgnated as Missiles in the same series at all? probably a fudge to make it seem as if its a lower risk/cost development to Congress compared to an all-new design and thus less liely to be canceled.