The ironic thing is that during the same period, 110V powered electric shavers - which most likely spurt out noise all over the RF spectrum - were perfectly acceptable to use on aircraft.
So, uh, apparently I was unaware of this rule: I used one about 35 years ago. I was flying to Europe, and didn’t have a compatible power adapter when I landed in Helsinki, so I used the plane’s lavatory on the hop to Sweden.