mc49, welcome to SCF. The 499 was perforated on a rotary perforator that was adjustable for spacing and this example was probable set at the minimum spacing.

Above is the rotary perforator. The top overarm shows the adjustable yokes for the rotary heads.
The 499f was the AEF booklet pane of 30. Only the middle horizontal row would be perforated aon all sides (9 stamps). These stamps would be indistinguishable from the regular 499 sheet stamps. (the plates were made from the same transfer rolls). A 499f booklet pane and the plate layout are shown below.

