I didn't buy a lot of NB size and regretted it as my girl was in NB size for 2 months and she came right on time and was 7 and a half pounds. She's a year old and can still fit 9 month onesies and 6 month pants. Every baby is different so you can't judge yours based on someone else's baby
I didn't buy any newborn clothes at all. Majority of my gifts from baby shower were 0-3m but everything I bought personally was 3m and up. I just feel like those first 3ms will fly by and they'll grow too quickly
My son wore newborn till 1.5 to almost 2 months. Didn't wear 0-3 months long 3 months now especially sleepers. But pants wise he still wears 0-3 small waist