Yes they can be a few pounds different, mine were saying he was going to be 10lb and came out a week late at 7lb 14oz!
Mine was very accurate to the gram. Honestly, it depends who’s doing it and how much the attention they are paying!
Yep they can be way off. My first was measuring small but not That small, like 20th centile or something. Then he was only 4lb 6oz when he was born
My LO was measuring 95th percentile at 35+6 when they scanned me. Came out at 75th percentile for weight and >99th percentile for length (7lb 3 and 57cm at 37+1)
Yes.