Im certain of when I got pregnant and baby is measuring a day ahead already as of last scan. They left my EDD. Babies grow at their own rate, some ahead some a little behind based on measurements. It’s normal.
I am a week behind what I thought I was when calculating LMP! But my midwife explained it is likely because I didn’t have a regular cycle even though I thought I did. You pretty much need to have a perfect 28 day cycle every month to accurately calculate using the LMP date. I am 12 weeks today but using my LMP I should be 13 xx
Sometimes the baby will grow faster or slower so that’s what could be causing the possible discrepancies