I’ve read that ICBMs are very hard to spot after the initial boost phase. That being the case, if I was an ICBM designer, I’d add a cold gas thruster to the payload stage that allowed the target to be adjusted or fine tuned while it was out of the atmosphere in a stealthy way — even a delta-V of just 100 m/s adds up to 280km when the missile takes 45 minutes to arrive.