I’m in the US but this was a while back, in the south. It was a highly ranked school and ended up producing lots of PhDs, but many of the families were blue collar and so there just wasn’t any awareness of things like this.
Nobody mentioned them in high school (1997) until I heard of them online and got my school to participate. 30 kids took the AHSME. Only one qualified for the AIME. And nobody qualified for IMO (though I tell myself I was close).
I believe the 1 in a million number.