I can't help feeling that the whole 'back in the day you wouldn't have known you were pregnant' thing is sometimes used as a stick to beat women with for their grief over early mc/to minimise the experience.
I've had six mc, ranging from five and a half to 9ish weeks. I knew I was pregnant every time. A regular cycle and no period is always going to make you wonder.
I find it interesting how the valuing of the baby as an entity worth acknowledging/protecting/mourning varies to suit the agenda - we are inreasingly told that women should (e.g.) abstain from alcohol if they are even onl trying to get pregnant, but then a loss before 12 weeks isn't regarded as the loss of a (potential) person to be mourned and there is even a cultural expectation to act (to the outside world) as if the baby doesn't exist before that magic milestone.
FWIW I didn't invest my miscarried babies with personhood in the sense of giving them names etc. And while awful, the losses weren't life-changingly, traumatically devastating in the way a stillbirth would be. But each mc was an intensely sad and difficult experience and not one that was easier to cope with by virtue of its minimisation.
To answer the OP's question, though, seeing as miscarriage means 'of recognised pregnancies' (i.e. not the non-implanted fertilised eggs some people upthread have been talking of), I am guessing it's not 'most' women who have had one (particularly as, as I know, some women have a lot more than their fair share of those 1 in 4 (ish) recognised pregnancies), but certainly a very sizeable minority.