Yes, my memory of 1978 to early 80's is the same as yours - hardly anyone got K.

But it picked up considerably in the second half of the 80's and through into the 90's. M started giving K himself, and after a little while he really got into it - he had K sessions quite often, and some of them were big. Then he let instructors give K again, at first only Belkis and Charnanand, then others.

So my guestimate is still 50k each in US and UK to about 1975, and then in the 30 years since probably another 50k - or OK, perhaps 40k - who knows (or cares), but something of that order. 30k would only be 1000 per year, and while some years were thin, as you say, some definitely were much more than that.