Older receptacles and even modern receptacles and cords do still make use of their holes.
It’s why if the holes are included there is specs they must follow.
This plug makes use of the holes for a solid mechanical connection that will only be removed when you pull on the collar to remove the pin that goes through the holes.
Not exactly a myth, but likely never used for retention purposes as was originally intended. See more here: https://electronics.stackexchange.com/questions/11495/nema-5-15p-blade-holes
Older receptacles and even modern receptacles and cords do still make use of their holes.
It’s why if the holes are included there is specs they must follow.
This plug makes use of the holes for a solid mechanical connection that will only be removed when you pull on the collar to remove the pin that goes through the holes.