One of the "holes" contains the town of Kidderminster. Looking at it on the full 25" map, that sheet is from the 1921 revision, the surrounding sheets are from the 1901 revision: https://maps.nls.uk/geo/explore/#zoom=17&lat=52.38277&lon=-2.24342&layers=168&b=7 Which may explain the holey map, as a record of which revision is where. Or not. Martin.