Disley is 1967, Kjellstrom is 1955. There have been revisions, but not enough. The others listed have not made it into the mainstream of orienteering literature. There is a wealth of good materials for instruction. Orienteering Skills and Strategies by Ron Lowry and Ken Sidney comes to mind quickly, but there are many more.
Every control has a code number or letter attached.
The code becomes part of the description and helps the competitor verify his location. This is especially necessary when courses of different levels are set in the same area and runners on one course are likely to stumble on to controls from another course. They put a pattern of holes in the card and verify his visit to the control site. Sending scouts into the woods with a pencil to write down control letters is dangerous, and pencils at the controls tend to break or get lost during the competition.