Adjusted age questions

I’m not really understanding the adjusted age stuff. I mean...I get how to calculate my son’s adjusted age. But what does it mean for milestones? Are his milestones set back? Like if his adjusted age is 0 weeks but he’s really 6 weeks old and babies start smiling around 8 weeks, does that mean he won’t start until closer to 14 weeks? I don’t mean to sound dumb - this is my first preemie so I don’t quite get it.