TurnItOff_OnAgainthis plug doesn't have the little holes
The holes are only for manufacturability.
Older plugs had a design that would hug the holes to hold the plug in place. It’s a holdover for people with older houses.
I think this fact is actually a myth, the holes are for manufacturing as stated previously.
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.