This is another unusual item for plate block collectors. There is a single plate number in the corner of the pane of stamps. However, the normal plate block of 4 doesn’t capture all 10 flag designs used. A plate block of 4 would only capture 2 of the designs. And because this is a fixed layout, the flags used in rows 3 through 8 would never appear in a plate block of 4.
Again, to capture all of the stamp designs, this issue is typically collected as a plate strip/20 so that all stamp designs are represented in the plate block.