I've just browsed some old safety videos on YouTube, and in the U.S. this recommendation seems to have appeared in the early 90s (e.g. Northwest 1993 https://yo

I've just browsed some old safety videos on YouTube, and in the U.S. this recommendation seems to have appeared in the early 90s (e.g. Northwest 1993 https://youtu.be/rUQtG0a_7d0?t=127 https://youtu.be/rUQtG0a_7d0?t=127), while being absent in the late 80s (e.g. Pan Am 1988 https://youtu.be/m3zj-oUm7vc?t=33 https://youtu.be/m3zj-oUm7vc?t=33).