they do tell you that, or they did me anyway, i wnet overdue with all 5 of mine and with ds3 i went to term plus 18, according to my dates, it was term plus 21 according to hospital dates, but i was very sure of my dates.
i still ended up being induced with all 5, and thankfuly with no2, 3 and 4 had good experiences. no 1 was a nightmare took 3 days and he was quite clearly not ready to born.
no 5 was also harder work, required the syntocin drip, with no 2-4 i just had my waters broken and that was fine. as it was the midwives checked my placentas after the births and in each case they said the placenta was fine, had lots of fluid and my babies were still vernixy and didnt look remotely overdue.
my mum also went to over 3wks late with meand my sister and we all ahve a longer menstrual cycle so i think i am just meant to cook babies for longer. however having waited so long with ds3 i decided to be induced at plus 15 with ds4, and with dd (no 5) i had had alot of stress at the end of pregnancy, serious illness of one of my children and i was run down and ill msyelf so was induced at term plus 10, bizarrely they didnt want to induce me then sa policy was plus 14. yet when i had ds1, ds2 and ds3 the policy had been plus 10 and i had to fight to go to term plus 14 and they went on about the risks etc, yet they had changed their minds by the time i had dd. as it was i had low fluid levels (got them to scan me) so they were happy to induce but my gut feeling with dd was that she needed to be born, whereas with my boys i knew they were well and all was fine, her labour was harder than the others tho and i think that was partly becuase my body needed another few days to be ready.
btw i actually had it written on my notes in BIG BOLD LETTERS, PATIENT HAS BEEN INFORMED OF THE RISKS OF STILL BIRTH when i went to term plus 14 with ds4, but by the time i had dd, 2yrs later THEY wanted me to go to term plus 14, despite me saying no i am worried about babies movements etc!