Weapons systems like the Tomahawk and HIMARS are continually evolved, especially the electronic systems like navigation and command+control. The iteration isn't nearly as fast as in other industries, but the modern incarnations are not 30+ years old, AFAIU, old stockpile notwithstanding.

That's also why they're so damned expensive, and why it's difficult for upstarts to break into the market with cheaper alternatives. Like any tech company, once they get the customer locked into a platform they're constantly pushing upgrades to both stay technologically competitive and, more importantly, keep their margins high.