The use specifically of a black square seems to occure multiple times for some entries.
Some of the holes are not square but rectangular.
1 All patterns are centered on the sheet along the reference edge.
2 The reference edge is always defined relative to a portrait orientation of the medium, regardless of the orientation
of the printed image or processing path.
3 The pattern axis offset is always specified relative to the reference edge.
4 The default pattern axis offset is always specified in points.
5 Thumbcuts are available in various standard shapes (labeled “No. N” where N is minimally ranging from 2..7).
“No. 3” seems to be the most widely used.
6 Single thumbcuts appear always in the center of the reference edge.
7 Oval-shaped holes sometimes actually look more like rectangular holes with rounded corners.
7++ A circle in the Shape column defines a round or eliptic hole and a square denotes a square or rectangular hole.
8 Generic hole types are dependent on the geographical area where the device is used.
<Remove all occurrences of double squares in Shape column>