Well I am currently over due with my first so I don't know about 3rd time babies.
My mum had 1 baby on it's due date and then the other 7 of us were always over due
When my mom had me she was 2 weeks over, then when she had my sister she was 2 weeks early, then with my brother she was 4 weeks later. She was 4 weeks later because her doctor was on vacation.
My first had her at 38 weeks second 40+3
All of mine were overdue, the third by 6 days...so for me it is normal to be overdue. They say that the third delivery can be tricky too, but mine was 2 hrs 50 mins and we stayed at home, no stiches and no problems at all, so that isnt always true, dont let anyone freak you out with those stories! Good luck! :)
Every pregnancy is different. Sounds like its not normal for you compared to your first 2 but every child has its own agenda. Isn't it always the 3rd child who is the rebel of the family? ;) that's what I heard.