Not everyone misses periods. My mum was almost 5 months gone before she knew she were pregnant with me - no symptoms, still bleeding monthly.
Some peoples periods are all over the place! When I was having dd (2001) there was a woman in next bed with pcos, fertility struggles, didn't know until she was 8.5 months! And yes 12 week scan for me then.
Even my first pregnancy in 1991 pregnancy tests were still quite expensive, not everyone bought them, I did as I was scared, I was single (had broken up with father a few weeks before), young (18) and living as a lodger. Women still didn't completely trust home tests (which were a bit more complex than poas then too) and went to dr for 'confirmation'. Home test was positive, but yes it was still very much the norm to go to dr to confirm. In my case I had confirmation one week, the following week had to go back to confirm mc. Definitely not like a "late period" very painful, lots of bleeding and clots. Not pleasant. But yes, I know not everyone's experiences are the same.
When you add in - women/girls not being taught about puberty, sex, conception it's really NOT surprising.
You may find this enlightening:
en.m.wikipedia.org/wiki/Clearblue
It was chemistry lab style test I had to use with first pregnancy.
"A quick Google says the first home tests were available in the mid-70s." Doesn't mean:
A They were available everywhere - look how long it takes even now for a newly designed/invented product to reach everywhere
B they were affordable for most, new products tend to be quite expensive until they become popular enough to justify mass production which reduces cost
C women were still quite self conscious about buying such products, they weren't just on a shelf in the supermarket like they are now - I went into the next town rather than buying in my village pharmacists - where the assistant KNEW EVERYONE - and worse Gossiped!
"For what purpose I can’t imagine." Changes to the cervix can indicate pregnancy, stage of pregnancy.
I was born in '72 my mother was told to stop smoking 'if possible' which she did - but she bf me for 6 wks then started again, stopped again when pregnancy confirmed for bro & sis, bf them for 6 weeks & Re-started. She was never a big drinker.