Interesting discussion.
In my first very accidental pregnancy where I didn't know dates, didn't have a clue if I missed AF, couldn't be 100% certain on when that whoopsie happened, do remember the "she'll be right"
I got one scan <gasp> at 20 weeks!!! GP didn't order a dating scan, just gave me an internal LOL he used to be an obstetrician. Was out on his dates by 1 week. Which my 20 weeks scan picked up on.
Amazing how much it's moved forwards to getting scans at the drop of a hat.