Originally Posted by
Jeff Wills
They make the welding area larger, strengthening the joint between the dropout and the chainstay/ seatstay.
I also think that this is the reason for the small sections of tubes (the two bigger holes on each side) in the dropout area - larger area for the welding.
The two smaller holes present only on the left side (above the seatstay) are clearly IS disc brake caliper mounts.