Answer by
LeheckaG (1826)
More-accurate UltraSound/EDDs are usually computer-estimated based on measuring various fetal dimensions via UltraSound-imaging and then comparing/correlating/extrapolating the measurements with a database of statistical measurement averages & sample prior actual delivery dates.
LMP/EDD predictions are usually less-accurate unless your cycles are REGULAR & EXACTLY 28 days.
If you had November "spotting" (less than a period),
it could have been implantation-light-bleeding.