Step 13: Registration pegs
The exact location you use for the pegs is up to you, but BE CONSISTENT. Every leaf needs to be able to mate with every other leaf.
If you have a horizontal boring machine, good for you. If not, you can build a jig to guide your hand-held drill bit into the edge. Clamp the jig to the edge of your board where you want to drill the hole, and let the hole in the jig guide your drill bit.
Drill two holes on each edge of every leaf, plus on the non-edging edge of the front top and rear leaf.
Add pegs to one edge of each leaf, including the rear leaf.
It helps if the pegs are slightly pointed as shown in the diagram. The photographs show one way to do this.