My baby wasnt a preemie but didnt smile til 8 weeks!
My little girl was born prematurely by 4 weeks and some milestones she’s been hitting 4 weeks later and some on time. Go by her corrected age which is technically only a newborn x
My son was born at 30+4 and he first smiled at exactly 16 weeks actual age so that’s 6/7 weeks corrected age.
Don't worry to much. Even baby had their own time to develop. My daughter didn't really had a full smile till like 6 or 7 months. Maybe a few flukes before that. She was 33 weeks preemie. Now 2 and nothing can stop her from doing anything now.