Kaz - I also remember my doctor advising me that the earlier 12 week scan is more accurate when determining a due date or date of conception, precisely for the the greater the variability in growth and development after this point. I am sure there would be more about this online.
The policy for induction at the royal women's is here if you are interested: Induction of Labour CPG
I have found it a very interesting read as my first bub was born 40 +14 (went into labour the day before) and I was due to attend an induction appointment on the day of my DS birth. I feel more informed about the process hospital's go through reading this info, just in case I have a long gestation with this bub too!