The hole is intended to simplify access to the screw for the gascolator bowl.
A batch of gear legs were modified during production (already in the production process when the design change was made).
Apparently the hole was accidentally added to the incorrect side.
If you have a leg with the hole on the wrong side, just add another hole in the same location, on the correct side (the updated production version will have a hole on each side to make sure the hole never ends up on the wrong side).
If you have a leg with no hole, contact Van's Tech Support. They can E-mail you a drawing depicting the proper location for the hole.