There is a question here on retrocomputing if round punch card holes where mechanically stiffer:
I wondered if the reason for the rectangular holes on IBM's 80-line punch card was not the readability of the punch cards themselves, but the durability of the punching tools used to make the holes.
A punching tool that should create rectangular holes only has to be sharpened on one side, like a chisel, and then it is sharp again. If you use four of these that are of triangular shape and combine them to a forming rectangle, you can create a nice, sharp, rectangular hole. And these four stamps could be sharpened very often, the longer the stamp tool, the more often that would be possible.
In the case of a round stamping die, the stamped piece is likely to be cut off first during manufacture, so that it is flat. In the next step, it gets an inner bore so that a hollow is created. The outsides thus become sharp for clean cuts, but these outer cutting edge wear out more quickly. Such a punch can then no longer be repaired with simple methods, but must be exchanged for a new one.
Is that perhaps the main reason why IBM used rectangular holes so that the stamping tools can be reground more often and last longer? A more detailed description of what the actual stamps looked like would be very revealing here. Macro Photos of the stamping tools would be super.
EDIT: In this video from university of Nottingham proof is given, that a lot of punching did wear out the punch tools: https://youtu.be/JafQYA7vV6s?t=114