Back when I was a student, in the 90s, I would frequently try and put up to 5kg above the limit (which was only 20kg then I believe) and nobody ever complained. But i rarely dared more.

I would instead often pack more weight in my hand luggage than in my hold luggage, since they did not weight it and thus there was truly no limit. My shoulders do not remember the 40kg dufflebag fondly. Of course, all sorts of glass bottles and liquids inside

For the worst, but most probably for the best, those days are long gone.